> ## Documentation Index
> Fetch the complete documentation index at: https://docs.slate-labs.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Customer Pay Existing Transaction

> Initiate a cashier session for an existing PENDING transaction.

Used by the webtrader to pay an already-created CHALLENGE_FEE /
CHALLENGE_RESET_FEE / CHALLENGE_ADDON_FEE transaction (created at
grant time by CRM or at self-enroll time). The tx already carries
`amount`/`currency`/`account_id`/`journey_id` — this endpoint stamps a
cashier_id, calls integration-service to create a payment session, and
returns the iframe/redirect config for the frontend to render.

The webhook handler (`payment_callback`) is unchanged: when the
cashier APPROVES the tx it dispatches to `activate_prop_account` /
`apply_addon_to_journey` based on `tx.type`. No money is moved here.



## OpenAPI

````yaml /openapi.json post /customers/me/transactions/{tx_id}/pay
openapi: 3.1.0
info:
  title: Slate API
  version: 1.0.0
  description: Trading infrastructure API.
servers:
  - url: https://api.{your-broker}.slate-labs.com
    variables:
      your-broker:
        default: broker
security: []
tags:
  - name: Authentication
  - name: API Tokens
  - name: Customers
  - name: Accounts
  - name: Orders
  - name: Instruments & Groups
  - name: Transactions
  - name: Payments
  - name: Transfers
  - name: Risk
  - name: Workflow & CRM
  - name: Messaging
  - name: Integrations
  - name: Webhooks
  - name: Compliance
  - name: Promo codes
  - name: Reporting
  - name: Audit
  - name: Fraud & moderation
  - name: Broker settings
  - name: Users
  - name: Roles & Teams
  - name: Streams (SSE)
  - name: Simulator
  - name: Observability
  - name: Prop trading
paths:
  /customers/me/transactions/{tx_id}/pay:
    post:
      tags:
        - Customers
      summary: Customer Pay Existing Transaction
      description: |-
        Initiate a cashier session for an existing PENDING transaction.

        Used by the webtrader to pay an already-created CHALLENGE_FEE /
        CHALLENGE_RESET_FEE / CHALLENGE_ADDON_FEE transaction (created at
        grant time by CRM or at self-enroll time). The tx already carries
        `amount`/`currency`/`account_id`/`journey_id` — this endpoint stamps a
        cashier_id, calls integration-service to create a payment session, and
        returns the iframe/redirect config for the frontend to render.

        The webhook handler (`payment_callback`) is unchanged: when the
        cashier APPROVES the tx it dispatches to `activate_prop_account` /
        `apply_addon_to_journey` based on `tx.type`. No money is moved here.
      operationId: >-
        customer_pay_existing_transaction_customers_me_transactions__tx_id__pay_post
      parameters:
        - name: tx_id
          in: path
          required: true
          schema:
            type: string
            format: uuid
            title: Tx Id
      responses:
        '200':
          description: Successful Response
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/CustomerDepositResponse'
        '422':
          description: Validation Error
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/HTTPValidationError'
components:
  schemas:
    CustomerDepositResponse:
      properties:
        transaction_id:
          type: string
          format: uuid
          title: Transaction Id
        gateway:
          type: string
          title: Gateway
        gateway_type:
          type: string
          title: Gateway Type
        currency:
          type: string
          title: Currency
        cashier_token:
          anyOf:
            - type: string
            - type: 'null'
          title: Cashier Token
        cashier_session_id:
          anyOf:
            - type: string
            - type: 'null'
          title: Cashier Session Id
        cashier_key:
          anyOf:
            - type: string
            - type: 'null'
          title: Cashier Key
        script_url:
          anyOf:
            - type: string
            - type: 'null'
          title: Script Url
        cashier_url:
          anyOf:
            - type: string
            - type: 'null'
          title: Cashier Url
        cashier_id:
          anyOf:
            - type: string
            - type: 'null'
          title: Cashier Id
        redirect_url:
          anyOf:
            - type: string
            - type: 'null'
          title: Redirect Url
      type: object
      required:
        - transaction_id
        - gateway
        - gateway_type
        - currency
      title: CustomerDepositResponse
      description: >-
        Returned after initiating a deposit — contains cashier iframe/redirect
        config.
    HTTPValidationError:
      properties:
        detail:
          items:
            $ref: '#/components/schemas/ValidationError'
          type: array
          title: Detail
      type: object
      title: HTTPValidationError
    ValidationError:
      properties:
        loc:
          items:
            anyOf:
              - type: string
              - type: integer
          type: array
          title: Location
        msg:
          type: string
          title: Message
        type:
          type: string
          title: Error Type
      type: object
      required:
        - loc
        - msg
        - type
      title: ValidationError

````