> ## Documentation Index > Fetch the complete documentation index at: https://docs.flipeet.io/llms.txt > Use this file to discover all available pages before exploring further. # Add test funds > Adds funds to your sandbox balance. New sandbox balances start with 10,000 USDC and 10,000 USDT. Sandbox keys only. ## OpenAPI ````yaml /api-reference/openapi.json post /api/v1/sandbox/balance/top-up openapi: 3.0.0 info: title: Flipeet Pay API version: '1.0' description: >- Accept and send stablecoin and local-currency payments. Authenticate with your secret key in the x-api-key header. Keys starting fpay_test_ use the sandbox; fpay_live_ moves real money. Guides: https://docs.flipeet.io contact: name: Flipeet Pay url: https://docs.flipeet.io servers: - url: https://api.pay.flipeet.io security: - x-api-key: [] tags: - name: Checkout description: >- Hosted payment pages: create a payment, send your customer to checkoutUrl, and get a webhook when they pay. - name: Deposits description: >- Collect stablecoins or local currency straight into your balance, with your own UI. - name: Balance description: What you hold, per asset. - name: Withdrawals description: Send funds from your balance to a wallet or a bank account. - name: Ramps description: >- Convert between local currency and stablecoins for your own customers, settled to their wallet or bank. - name: Webhooks description: Delivery history, resends and test events. - name: Sandbox description: 'Test-mode tools: simulate outcomes and add test funds. Sandbox keys only.' paths: /api/v1/sandbox/balance/top-up: post: tags: - Sandbox summary: Add test funds description: >- Adds funds to your sandbox balance. New sandbox balances start with 10,000 USDC and 10,000 USDT. Sandbox keys only. operationId: SandboxController_topUp parameters: [] requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/TopUpDto' example: asset: usdc amount: 5000 responses: '200': description: Sandbox balance topped up. content: application/json: schema: type: object properties: message: type: string example: Successful status: type: string example: success statusCode: type: number example: 200 data: type: array items: type: object properties: currency: type: string example: cngn available: type: number example: 0 example: message: Successful status: success statusCode: 200 data: - currency: cngn available: 0 - currency: usdc available: 15000 - currency: usdt available: 10000 '400': $ref: '#/components/responses/Error400' '401': $ref: '#/components/responses/Error401' '403': $ref: '#/components/responses/Error403' '429': $ref: '#/components/responses/Error429' '500': $ref: '#/components/responses/Error500' security: - x-api-key: [] components: schemas: TopUpDto: type: object properties: asset: type: string enum: - usdc - usdt - cngn example: usdc description: The stablecoin to add. amount: type: number example: 5000 description: How much to add, up to 1,000,000. required: - asset - amount responses: Error400: description: The request is invalid. `details.errors` lists every problem. content: application/json: schema: type: object properties: message: type: string description: What went wrong, for people. May be reworded. status: type: string example: error statusCode: type: integer description: The HTTP status. code: type: string description: A stable code to branch on. enum: - invalid_request - authentication_failed - permission_denied - not_found - conflict - rate_limited - internal_error - provider_error details: type: object nullable: true description: For validation errors, `errors` lists every problem. requestId: type: string description: Quote it when you contact us. timestamp: type: string format: date-time example: message: Amount must be a positive number status: error statusCode: 400 code: invalid_request details: errors: - Amount must be a positive number requestId: req_5f0c2a9b8d7e4c1f9a3b6d2e1c0f7a8b timestamp: '2026-11-04T10:00:00.000Z' Error401: description: The API key is missing, mistyped or revoked. content: application/json: schema: type: object properties: message: type: string description: What went wrong, for people. May be reworded. status: type: string example: error statusCode: type: integer description: The HTTP status. code: type: string description: A stable code to branch on. enum: - invalid_request - authentication_failed - permission_denied - not_found - conflict - rate_limited - internal_error - provider_error details: type: object nullable: true description: For validation errors, `errors` lists every problem. requestId: type: string description: Quote it when you contact us. timestamp: type: string format: date-time example: message: Invalid or inactive API key status: error statusCode: 401 code: authentication_failed details: null requestId: req_5f0c2a9b8d7e4c1f9a3b6d2e1c0f7a8b timestamp: '2026-11-04T10:00:00.000Z' Error403: description: This key can't do this. content: application/json: schema: type: object properties: message: type: string description: What went wrong, for people. May be reworded. status: type: string example: error statusCode: type: integer description: The HTTP status. code: type: string description: A stable code to branch on. enum: - invalid_request - authentication_failed - permission_denied - not_found - conflict - rate_limited - internal_error - provider_error details: type: object nullable: true description: For validation errors, `errors` lists every problem. requestId: type: string description: Quote it when you contact us. timestamp: type: string format: date-time example: message: Sandbox endpoints need a sandbox key (fpay_test_…) status: error statusCode: 403 code: permission_denied details: null requestId: req_5f0c2a9b8d7e4c1f9a3b6d2e1c0f7a8b timestamp: '2026-11-04T10:00:00.000Z' Error429: description: Too many requests. Each key can make 120 a minute. content: application/json: schema: type: object properties: message: type: string description: What went wrong, for people. May be reworded. status: type: string example: error statusCode: type: integer description: The HTTP status. code: type: string description: A stable code to branch on. enum: - invalid_request - authentication_failed - permission_denied - not_found - conflict - rate_limited - internal_error - provider_error details: type: object nullable: true description: For validation errors, `errors` lists every problem. requestId: type: string description: Quote it when you contact us. timestamp: type: string format: date-time example: message: Too many requests. Slow down and try again shortly. status: error statusCode: 429 code: rate_limited details: null requestId: req_5f0c2a9b8d7e4c1f9a3b6d2e1c0f7a8b timestamp: '2026-11-04T10:00:00.000Z' Error500: description: Something went wrong on our side. Retry with backoff. content: application/json: schema: type: object properties: message: type: string description: What went wrong, for people. May be reworded. status: type: string example: error statusCode: type: integer description: The HTTP status. code: type: string description: A stable code to branch on. enum: - invalid_request - authentication_failed - permission_denied - not_found - conflict - rate_limited - internal_error - provider_error details: type: object nullable: true description: For validation errors, `errors` lists every problem. requestId: type: string description: Quote it when you contact us. timestamp: type: string format: date-time example: message: Internal server error status: error statusCode: 500 code: internal_error details: null requestId: req_5f0c2a9b8d7e4c1f9a3b6d2e1c0f7a8b timestamp: '2026-11-04T10:00:00.000Z' securitySchemes: x-api-key: type: apiKey in: header name: x-api-key description: >- Your secret key. `fpay_test_…` keys use the sandbox; `fpay_live_…` keys move real money. ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.