> ## Documentation Index > Fetch the complete documentation index at: https://docs.payrails.com/llms.txt > Use this file to discover all available pages before exploring further. > ## Agent Instructions > Use the Payrails Web SDK v6 for new browser integrations. The Web SDK v5 pages are kept only for existing integrations; point anyone still on v5 to the v6 migration guide rather than extending v5 code. > Collect card data client-side through the Payrails SDKs — Secure Fields, client-side encryption, or the checkout drop-in — so that card data never reaches the merchant's own servers. Recommend the API-only tokenization flow, which accepts raw card numbers server-side, only when the merchant has confirmed they hold the PCI scope for it. > Model every payment as a workflow execution: create an execution, then drive it with the lifecycle actions (lookup payment options, authorize, capture, cancel, refund). Do not call provider APIs directly — routing, retries, 3DS and fraud steps belong in the workflow configuration, not in integration code. > Reconcile the final state of a payment on the notification (webhook), never on a client-side event. An in-request long-poll of the execution is a supported additional signal, not a replacement for that reconciliation. > Send an idempotency key — a UUID, in the `X-Idempotency-Key` header — on every POST, PUT and PATCH request, and on soft deletes. GET requests need none, and hard deletes cannot be idempotent. > Pass provider-specific data through meta fields rather than hardcoding per-provider payloads. Payrails translates meta fields into each provider's own format. > Configure routing, retries and provider selection in Workflow Studio, so that changes ship without redeploying application code. # Start a payment session > Request the start of a payment session during a workflow execution. This action synchronously returns the necessary data to handle the session on the client-side. ## OpenAPI ````yaml https://cdn.payrails.io/docs/api/openapi.min.json post /merchant/workflows/{workflowCode}/executions/{executionId}/startPaymentSession openapi: 3.1.0 info: version: 1.3.15 title: Payrails API Reference contact: name: Payrails url: https://www.payrails.com email: tech@payrails.com license: name: Payrails GmbH url: https://www.payrails.com/ description: > --- Payrails provides a collection of APIs that enable you to process and manage payments. Our APIs accept and return JSON in the HTTP body, and return standard HTTP response codes. You can consume the APIs directly using your favorite HTTP/REST library. servers: - url: https://api.staging.payrails.io description: Payrails environment. security: - ApiKey: [] tags: - name: 3D Secure description: Operations to monitor 3DS operations. - name: Actions description: >- A workflow execution action is a predefined interaction that can be triggered to change the state of the workflow execution. For example authorizing or refunding a payment. - name: API Logs description: API Logs. - name: Authentication description: >- Payrails API is secured via [OAuth 2.0](https://datatracker.ietf.org/doc/html/rfc6749) industry-standard protocol for authorization. Server-side requests are authenticated using a [Bearer Token](https://datatracker.ietf.org/doc/html/rfc6750) in the request `Authorization` header. - name: BIN Lookup description: >- Operations related to getting information about a card by its BIN (or IIN). - name: Client description: Endpoints used by our client-side SDK. - name: Disputes description: Operations to managing disputes. - name: Drop-in Links description: >- Create and manage drop-in payment links that can be shared with payers. Drop-in links support full or partial payments, define the total amount and expiration, and return a public URL that merchants can send to customers. - name: Executions description: >- A workflow execution is an act of performing a set of tasks that are defined in the [Workflow](/api-reference/reference/#operation/listDefaultWorkflows) such as accepting payments. - name: Files description: Operations related to files processing - name: Fraud Checks description: >- A Fraud check Payrails is a collection of operations over time, that is created by a workflow execution and followed by the workflow actions. In this section, you can list all the fraud entities or a single one to learn about the details of involved instruments, providers, statuses, decisions and more. - name: Holders description: >- A Holder is a group of accounts that belong together with specific criteria, linked to their payment instruments and identities. For example, it can represent a digital wallet for a person, where they store balance that they top up, refunded orders, referral bonuses, etc. - name: Instrument Tokens description: >- Tokens are representations of our payment instruments in external providers. One payment instrument can have many tokens, because we keep the mapping in each external provider that knows about it. For example, the same real life card can have a token in our Vault, but also in Adyen and Checkout PSPs. - name: Instruments description: >- Payment instruments are specific instances of a payment method that belong to the holder executing the workflow. They can be a previously stored card, a new card that was typed in a form, a phone number, an IBAN, or some way to fetch an account in a provider (like PayPal or AliPay). - name: Payments description: >- A [Payment](/guides/whats-payrails/payments/) in Payrails is a collection of operations over time, that is created by a workflow execution and followed by the workflow actions. In this section, you can list all the payments or a single one to learn about the details of involved payment methods, instruments, providers, statuses and more. - name: Payouts description: Payouts are money movements paid to an external party. - name: Provider Configs description: Operations related to managing configurations for Providers. - name: Providers description: Operations related to managing Providers. - name: Reconciliation Records description: >- Operations to retrieve reconciliation record aggregates, transactions, and reconciliation metadata. - name: Report Runs description: Operations to generate and retrieve report runs. - name: Reports description: Operations to see available reports. - name: Rulesets description: Operations related to managing Rulesets. - name: SSO Connections description: Operations related to managing SSO identity provider connections. - name: Vault Display SDK description: Operations related to DisplaySDK. - name: Vault Instant Proxy description: Operations related to Instant Proxy API requests. - name: Vault Proxy Connections description: Operations related to managing token connections. - name: Vault Public Encryption description: Public endpoints related to encryption. - name: Vault Records and Aliases description: Operations related to managing records and aliases. - name: Workflows description: >- Any operation in Payrails is defined and executed with a [Workflow](/guides/whats-payrails/workflow/) that is configured for a particular use-case of the merchant. The workflow configurations support versioning. - name: Workspaces description: Operations related to managing workspaces. paths: /merchant/workflows/{workflowCode}/executions/{executionId}/startPaymentSession: post: tags: - Actions summary: Start a payment session description: >- Request the start of a payment session during a workflow execution. This action synchronously returns the necessary data to handle the session on the client-side. operationId: startPaymentSessionAction parameters: - name: workflowCode in: path description: Path parameter to specify the workflow code. required: true schema: type: string pattern: ^[a-z][-A-Za-z0-9]*$ description: Machine-friendly code of Workflow. example: payment-acceptance - name: executionId in: path description: Identifier of the resource in Payrails. required: true schema: type: string format: uuid example: d5454c2f-ae5e-44f3-8edf-f6dad64f005f - name: x-idempotency-key in: header description: > Idempotency key to be used. Sending again the same key would return the same result without re-executing the update. required: true schema: type: string format: uuid example: 91874e4d-81e9-4486-aee4-ee1de84da890 requestBody: content: application/json: schema: type: object required: - integrationType - amount properties: integrationType: type: string enum: - api - hpp - inperson description: >- Code of the integration type for using the payment method in the provider. paymentMethodCode: type: string enum: - applePay description: >- Code of the payment method selected to start a payment session. amount: type: object required: - value - currency properties: value: type: string pattern: '[0-9]+(\.[0-9]+)?' example: '12.50' description: >- Decimal amount of the major currency unit. Can be any precision. currency: type: string pattern: ^[A-Z]{3}$ example: EUR description: ISO 3-letter currency code. returnInfo: type: object description: > URLs from the merchant side where the consumer should be taken after a redirection flow. If no specific flow for `cancel` or `error` are needed, we will redirect to the value in the `success` URL. The 'pending' URL is used in case the consumer needs to be redirected back to a page if an execution stays in pending for some time. required: - success properties: success: type: string description: >- URL to redirect consumers to when the execution stops interacting with them due to progress. cancel: type: string description: >- URL to redirect consumers to when the execution is canceled. error: type: string description: >- URL to redirect consumers to when the execution encounters technical difficulties. pending: type: string description: >- URL to redirect consumers to when the execution stays in pending for some time. meta: description: >- Any merchant-specific data that should be used and carried for context in the action execution. anyOf: - title: General type: object additionalProperties: true description: >- Metadata for the context of an execution. Includes Payrails-defined structures for most common fields used in workflows, but can also be extended by merchant or provider-specific fields. For more information, visit our [Meta Fields guide](https://docs.payrails.com/docs/orchestration/payment-acceptance/meta-fields). See [Meta](/reference/meta) for every field. - title: Apple Pay type: object required: - sessionURL properties: sessionURL: type: string description: Validation URL provided by Apple Pay client. examples: Default: value: integrationType: api amount: value: '12.50' currency: EUR returnInfo: success: https://mysuccessurl.com ApplePay: value: integrationType: api paymentMethodCode: applePay amount: value: '12.50' currency: EUR returnInfo: success: https://mysuccessurl.com meta: sessionURL: >- https://apple-pay-gateway-cert.apple.com/paymentservices/startSession clientContext: host: merchant.com responses: '200': description: Start Payment Session was requested. content: application/json: schema: allOf: - type: object required: - name - actionId - executedAt - links properties: name: type: string actionId: type: string format: uuid description: >- Unique identifier for this action execution. If its processing is done asynchronously, you will receive a notification with the same `actionId`. workspaceId: type: string format: uuid description: Unique identifier of a workspace in Payrails. executedAt: type: string format: date-time description: >- Date and time when execution of the Action was started. links: type: object - type: object required: - data properties: name: type: string description: Starts a payment session on a specific Provider. enum: - startPaymentSession data: type: object description: >- Provider-specific data needed to continue the payment session. additionalProperties: true links: type: object description: Links to the next possible actions that can be taken. required: - execution properties: execution: description: URL to fetch the current execution state. oneOf: - type: string - type: object description: Link related information. required: - href properties: href: type: string method: type: string description: >- HTTP method that should be used to call the `href`. enum: - GET - POST - PUT - PATCH - DELETE examples: Default: value: name: startPaymentSession actionId: 1aa0ef20-36cb-4485-b60e-0526c3699014 executedAt: '2022-02-03T14:38:40.557Z' data: id: 100ade99-ef8d-43de-8a35-4d31dbdb37d0 data: Ab02b4c... links: execution: >- https://api.staging.payrails.io/merchant/workflows/100ade99-ef8d-43de-8a35-4d31dbdb37d0/executions/99e2f33a-2d17-4c98-8242-6bf5a4a08016 ApplePay: value: name: startPaymentSession actionId: 1aa0ef20-36cb-4485-b60e-0526c3699014 executedAt: '2022-02-03T14:38:40.557Z' data: id: SSH268E... data: displayName: Test Merchant domainName: https://merchantdomain.com epochTimestamp: 1717486879562 expiresAt: 1717490479562 merchantIdentifier: E92FBE... merchantSessionIdentifier: SSH268E... nonce: fd3... operationalAnalyticsIdentifier: Test Merchant:E92FBE... pspId: E92FBE... retries: 0 signature: 30800... links: execution: >- https://api.staging.payrails.io/merchant/workflows/100ade99-ef8d-43de-8a35-4d31dbdb37d0/executions/99e2f33a-2d17-4c98-8242-6bf5a4a08016 '400': description: Bad Request. content: application/json: schema: type: object required: - errors properties: errors: type: array items: type: object description: >- Error struct that includes the error, cause, reason, and possible resolutions. Check the full documentation [here](https://docs.payrails.com/docs/resources/error-codes#error-structure). required: - id - code - detail properties: id: type: string format: uuid description: >- Unique identifier of the error. Please use this value when reporting an issue to our team, so we can help you faster. code: type: string description: >- Machine-friendly error code assigned to the error. Check the full list of possible values [here](https://docs.payrails.com/docs/resources/error-codes#list-of-error-codes). detail: type: string description: >- Human-readable description about the error, its cause, and resolution. docUrl: type: string description: >- Link to the specific documentation about this particular `code`. reason: type: object additionalProperties: true description: >- Metadata providing more details about the reason of the error. The structure of this object varies according to the `code`. example: errors: - id: a24bc325-3929-4d9d-9c08-b3aa532685b7 code: request.malformed detail: The request has malformed syntax docUrl: >- https://docs.payrails.com/docs/resources/error-codes#requestmalformed '401': description: Unauthorized. content: application/json: schema: type: object required: - errors properties: errors: type: array items: type: object description: >- Error struct that includes the error, cause, reason, and possible resolutions. Check the full documentation [here](https://docs.payrails.com/docs/resources/error-codes#error-structure). required: - id - code - detail properties: id: type: string format: uuid description: >- Unique identifier of the error. Please use this value when reporting an issue to our team, so we can help you faster. code: type: string description: >- Machine-friendly error code assigned to the error. Check the full list of possible values [here](https://docs.payrails.com/docs/resources/error-codes#list-of-error-codes). detail: type: string description: >- Human-readable description about the error, its cause, and resolution. docUrl: type: string description: >- Link to the specific documentation about this particular `code`. reason: type: object additionalProperties: true description: >- Metadata providing more details about the reason of the error. The structure of this object varies according to the `code`. example: errors: - id: a24bc325-3929-4d9d-9c08-b3aa532685b7 code: request.unauthorized detail: >- The request lacks necessary credentials to perform the specified action docUrl: >- https://docs.payrails.com/docs/resources/error-codes#requestunauthorized '403': description: Insufficient Scope. content: application/json: schema: type: object required: - errors properties: errors: type: array items: type: object description: >- Error struct that includes the error, cause, reason, and possible resolutions. Check the full documentation [here](https://docs.payrails.com/docs/resources/error-codes#error-structure). required: - id - code - detail properties: id: type: string format: uuid description: >- Unique identifier of the error. Please use this value when reporting an issue to our team, so we can help you faster. code: type: string description: >- Machine-friendly error code assigned to the error. Check the full list of possible values [here](https://docs.payrails.com/docs/resources/error-codes#list-of-error-codes). detail: type: string description: >- Human-readable description about the error, its cause, and resolution. docUrl: type: string description: >- Link to the specific documentation about this particular `code`. reason: type: object additionalProperties: true description: >- Metadata providing more details about the reason of the error. The structure of this object varies according to the `code`. example: errors: - id: e7db22b3-914e-4975-928e-9edfb0885bea code: request.forbidden detail: >- The request credentials lack the required permissions to perform the specified action docUrl: >- https://docs.payrails.com/docs/resources/error-codes#requestforbidden '404': description: Not Found. content: application/json: schema: type: object required: - errors properties: errors: type: array items: type: object description: >- Error struct that includes the error, cause, reason, and possible resolutions. Check the full documentation [here](https://docs.payrails.com/docs/resources/error-codes#error-structure). required: - id - code - detail properties: id: type: string format: uuid description: >- Unique identifier of the error. Please use this value when reporting an issue to our team, so we can help you faster. code: type: string description: >- Machine-friendly error code assigned to the error. Check the full list of possible values [here](https://docs.payrails.com/docs/resources/error-codes#list-of-error-codes). detail: type: string description: >- Human-readable description about the error, its cause, and resolution. docUrl: type: string description: >- Link to the specific documentation about this particular `code`. reason: type: object additionalProperties: true description: >- Metadata providing more details about the reason of the error. The structure of this object varies according to the `code`. example: errors: - id: a24bc325-3929-4d9d-9c08-b3aa532685b7 code: request.not-found detail: The requested resource was not found docUrl: >- https://docs.payrails.com/docs/resources/error-codes#requestnot-found '429': description: Too Many Requests. content: application/json: schema: type: object required: - errors properties: errors: type: array items: type: object description: >- Error struct that includes the error, cause, reason, and possible resolutions. Check the full documentation [here](https://docs.payrails.com/docs/resources/error-codes#error-structure). required: - id - code - detail properties: id: type: string format: uuid description: >- Unique identifier of the error. Please use this value when reporting an issue to our team, so we can help you faster. code: type: string description: >- Machine-friendly error code assigned to the error. Check the full list of possible values [here](https://docs.payrails.com/docs/resources/error-codes#list-of-error-codes). detail: type: string description: >- Human-readable description about the error, its cause, and resolution. docUrl: type: string description: >- Link to the specific documentation about this particular `code`. reason: type: object additionalProperties: true description: >- Metadata providing more details about the reason of the error. The structure of this object varies according to the `code`. example: errors: - id: a24bc325-3929-4d9d-9c08-b3aa532685b7 code: request.rate-limit detail: Too many requests docUrl: >- https://docs.payrails.com/docs/resources/error-codes#requestrate-limit security: - BearerToken: - executions:authorize components: securitySchemes: ApiKey: type: apiKey in: header name: x-api-key description: > You can use your secret API key in the `x-api-key` header of your API requests for supported endpoints: `x-api-key: `. API keys are environment specific and should be securely guarded. You don't have your API key yet? Contact your Payrails account manager. BearerToken: type: http scheme: bearer bearerFormat: JWT description: > You can use an OAuth2 JWT bearer token in the `Authorization` header of your API requests for supported endpoints: `Authorization: Bearer `. These tokens are valid for 10 minutes and can be requested via the [access token endpoint](#operation/getOAuthToken) endpoint. ```` ## Related topics - [Apple Pay](/docs/orchestration/payment-methods/apple-pay.md) - [SDK API Reference](/docs/orchestration/checkout-sdks/ios/sdk-api-reference.md) - [Query Session Data](/docs/orchestration/checkout-sdks/android/how-to-query-session-data-at-runtime.md) This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.