> ## Documentation Index > Fetch the complete documentation index at: https://docs.knotapi.com/llms.txt > Use this file to discover all available pages before exploring further. # Checkout > Checkout a user's merchant cart. ## OpenAPI ````yaml POST /cart/checkout openapi: 3.1.0 info: title: Knot API description: An API to interact with the Knot merchant connectivity platform. version: 1.0.0 servers: - url: https://development.knotapi.com description: Development server security: - basicAuth: [] paths: /cart/checkout: post: description: Checkout a user's merchant cart. operationId: checkout requestBody: description: The input parameters required to checkout a cart. content: application/json: schema: type: object properties: external_user_id: type: string description: Your unique identifier for the user. example: abc123 merchant_id: type: integer description: Unique identifier for the merchant. example: 456 payment_method: type: object properties: id: type: string description: Your unique identifier for the payment method. example: 81n9al10a0ayn13 jwe: type: string description: >- JWE value of the `user` and `card` objects. Created using the public key retrieved from [Retrieve JWK](https://docs.knotapi.com/api-reference/products/card-switcher/retrieve-jwk) example: eyJhbGciOiJSU0EtT0FFUC0yNTYiLC... is_single_use: type: boolean description: Whether the payment method is single-use only. example: true default: false required: - id - jwe - is_single_use simulate: description: Simulate a failure in the development environment. oneOf: - type: string enum: - failed description: The checkout attempt fails. example: failed required: - external_user_id - merchant_id responses: '202': description: Successful request. content: application/json: schema: type: object properties: message: type: string description: Success message. example: Success '400': description: Bad request. content: application/json: schema: $ref: '#/components/schemas/Error' examples: UserNotFound: summary: User was not found value: error_type: USER_ERROR error_code: USER_NOT_FOUND error_message: >- The user was not found. Please check the external_user_id provided. MerchantAccountNotFound: summary: Merchant account was not found value: error_type: MERCHANT_ACCOUNT_ERROR error_code: MERCHANT_ACCOUNT_NOT_FOUND error_message: >- The merchant account was not found. Please check the merchant_id provided. CartNotFound: summary: Cart was not found value: error_type: CART_ERROR error_code: CART_NOT_FOUND error_message: >- The cart was not found. Please ensure you synced the cart recently. MerchantAccountDisconnected: summary: Merchant account is disconnected value: error_type: MERCHANT_ACCOUNT_ERROR error_code: MERCHANT_ACCOUNT_DISCONNECTED error_message: >- The merchant account is disconnected. Please check the merchant_id provided. MerchantUnavailable: summary: Merchant is not available value: error_type: MERCHANT_ERROR error_code: MERCHANT_UNAVAILABLE error_message: >- The merchant is unavailable. Please check the merchant_id provided. MerchantIdRequired: summary: merchant_id field is required value: error_type: INVALID_REQUEST error_code: INVALID_FIELD error_message: The merchant_id field is required. ExternalUserIdRequired: summary: external_user_id is required value: error_type: INVALID_REQUEST error_code: INVALID_FIELD error_message: The external user id field is required. PaymentMethodFieldRequired: summary: ID is missing in payment_method value: error_type: INVALID_REQUEST error_code: INVALID_FIELD error_message: >- The payment_method.id field is required when payment_method is provided. UserFieldRequired: summary: User object field required value: error_type: INVALID_REQUEST error_code: INVALID_JWE error_message: The user.phone number is required. CardNumberNotNumeric: summary: Card number not numeric. value: error_type: INVALID_REQUEST error_code: INVALID_JWE error_message: The card.number must be numeric. CardNumberTooLong: summary: Card number too long. value: error_type: INVALID_REQUEST error_code: INVALID_JWE error_message: The card.number is too long for card type. CardNumberTooShort: summary: Card number too short. value: error_type: INVALID_REQUEST error_code: INVALID_JWE error_message: The card.number is too short for card type. CardNumberInvalid: summary: Card number invalid. value: error_type: INVALID_REQUEST error_code: INVALID_JWE error_message: >- The card.number is invalid and does not pass the Luhn check. CVVNotNumeric: summary: CVV not numeric value: error_type: INVALID_REQUEST error_code: INVALID_JWE error_message: The card.cvv must be numeric. CVVTooLong: summary: CVV to long. value: error_type: INVALID_REQUEST error_code: INVALID_JWE error_message: The card.cvv is too long for card type. CVVTooShort: summary: CVV to short. value: error_type: INVALID_REQUEST error_code: INVALID_JWE error_message: The card.cvv is too short for card type. CVVRequired: summary: CVV is required. value: error_type: INVALID_REQUEST error_code: INVALID_JWE error_message: The card.cvv is required. CardExpirationInvalid: summary: Card expiration invalid. value: error_type: INVALID_REQUEST error_code: INVALID_JWE error_message: The card.expiration should be in MM/YYYY or MM/YY format. CardExpired: summary: Card expired. value: error_type: INVALID_REQUEST error_code: INVALID_JWE error_message: The card is expired. InvalidJWE: summary: JWE invalid. value: error_type: INVALID_REQUEST error_code: INVALID_JWE error_message: The jwe is invalid. OngoingOperation: summary: There is an existing operation value: error_type: MERCHANT_ACCOUNT_ERROR error_code: ONGOING_OPERATION error_message: An existing operation is in progress. '401': description: Unauthorized request. content: application/json: schema: $ref: '#/components/schemas/Error' examples: AuthFailed: summary: Auth failed value: error_type: INVALID_INPUT error_code: INVALID_API_KEYS error_message: Invalid client_id or secret provided. '403': description: Forbidden request. content: application/json: schema: $ref: '#/components/schemas/Error' examples: NoAccess: summary: No access value: error_type: INVALID_REQUEST error_code: NO_ACCESS error_message: Please contact Knot for access to this endpoint. '500': description: Internal server error. content: application/json: schema: $ref: '#/components/schemas/Error' examples: InternalServerError: summary: Unexpected server error value: message: Server Error components: schemas: Error: type: object properties: error_type: type: string description: Type of error. enum: - INVALID_INPUT - INVALID_REQUEST - USER_ERROR - SESSION_ERROR - MERCHANT_ACCOUNT_ERROR - MERCHANT_ERROR - SUBSCRIPTION_ERROR - TRANSACTION_ERROR - CART_ERROR example: INVALID_REQUEST error_code: type: string description: Error code. enum: - INVALID_API_KEYS - INVALID_FIELD - INVALID_JWE - INVALID_CURSOR_FORMAT - USER_NOT_FOUND - MERCHANT_ACCOUNT_NOT_FOUND - MERCHANT_ACCOUNT_DISCONNECTED - SESSION_NOT_FOUND - EXTEND_NOT_SUPPORTED - MERCHANT_UNAVAILABLE - NO_ACCESS - TRANSACTION_NOT_FOUND - NO_TRANSACTIONS - SUBSCRIPTION_NOT_FOUND - ONGOING_OPERATION - CART_NOT_FOUND - FULFILLMENT_NOT_FOUND example: INVALID_FIELD error_message: type: string description: Detailed error message. example: The limit may not be greater than 10. securitySchemes: basicAuth: type: http scheme: basic description: >- Basic authentication header of the form `Basic `, where `` is the base64-encoded string `username:password`. Use your `client_id` as the `username` and your `secret` as the `password` value. ````