> ## Documentation Index > Fetch the complete documentation index at: https://docs.pay.aptahq.com/llms.txt > Use this file to discover all available pages before exploring further. # Convert between your own wallets — money moves > **Actually convert money between two of your own wallets.** The use case is funding a corridor you are short on: you hold UGX, you need to pay out in KES, so you exchange first and then send. Also how a treasury process rebalances float across currencies. To be clear about what this is NOT: it moves money **between your own wallets only**. It never sends money to a customer — that is `POST /v1/payouts`, which handles its own cross-currency conversion via `amount_type`. You do not need to call this before a cross-currency payout. Converts `amount` of `from` into `to` between wallets you already hold. **This moves money**, so `Idempotency-Key` is REQUIRED; a missing one is a 400 and the server never invents one. ONE call. The provider's quote-then-execute handshake happens INTERNALLY and that two-call shape never leaks to you — which is also what keeps the ~60s quote window from being your problem. You do not need to call `/v1/fx/quote` first; that endpoint exists to show a price in a UI. Replaying a completed key returns the original response verbatim with no second conversion. The same key with different parameters is a 422. `rate` in the response is the rate the executed quote encoded — the one actually applied — not a figure recomputed from the returned amounts. **The source wallet must be funded.** The provider prices a conversion it cannot fund but issues no token to execute it, which surfaces here as a 409 `quote_not_executable`. It is terminal: retrying will not help until the wallet holds enough of `from`. `/v1/fx/quote` still returns the rate in that state, so a quote succeeding is not evidence that an exchange will. ## OpenAPI ````yaml /openapi.json post /v1/fx/exchange openapi: 3.0.3 info: title: AptaPay Gateway version: 1.0.0 description: > One provider-neutral payment API owned by many apps: collections, payouts, bank resolution and FX, with signed webhooks back. ## Authentication Every `/v1/*` request carries four headers. **A plain API key is not enough** — a key in a proxy log or an error report would be immediately usable, whereas a signature binds the request to a body and a moment. | Header | Value | | --- | --- | | `X-AptaPay-Key` | `{app_id}.{key_id}.{api_key}` | | `X-AptaPay-Timestamp` | unix seconds | | `X-AptaPay-Nonce` | 16-64 chars, `[A-Za-z0-9_-]`, unique per request | | `X-AptaPay-Signature` | `v1={hex HMAC-SHA256}` | The signature is HMAC-SHA256, with your **inbound** signing secret, over exactly these ten fields joined by `\n`: ``` v1 {APP_ID} {KEY_ID} {HOST} lowercased {METHOD} uppercased {PATH} no query, NOT url-decoded {CANONICAL_QUERY} sorted, RFC3986-encoded, "" when absent {TIMESTAMP} {NONCE} {SHA256_HEX(RAW_BODY)} sha256("") for GET/DELETE ``` Every field earns its place. `CANONICAL_QUERY` is in there because without it `?limit=1` and `?limit=100000` sign identically, so a captured read signature could be replayed to dump everything. `HOST` stops a signature captured against one deployment replaying into another. The timestamp window is **asymmetric**: `-120s <= now - ts <= +30s`. A symmetric window is a ten-minute replay window, and there is no legitimate reason to sign in the future beyond small clock skew. A working reference implementation is in `docs/TENANT_INTEGRATION.md`, and `scripts/sign_request.mjs` signs a request from the terminal. ## Idempotency `Idempotency-Key` is **required** on every money-moving POST. A missing key is a 400 — the server never invents one, because a server-generated key is unique per request and protects nothing, which is worse than none because it looks like protection. - Replaying a completed key returns the **original response verbatim**, with its original status code. No second provider call. - The same key with **different parameters** is a 422, never a replay. - A concurrent duplicate is a 409 `request_in_progress`. ## Errors Branch on `error.code` and the three booleans, never on the HTTP status: `terminal` (reverse and tell the user), `retriable` (retry with the same key), `ambiguous` (**do not reverse** — poll instead). ## Amounts Integer minor units, with a per-currency exponent. **UGX, RWF, XAF and XOF are zero-decimal**: 2000 UGX is `2000`. Getting this wrong is a 100x error. ## Test mode is NOT a sandbox **Every request reaches a real provider. There is no sandbox, and no test host.** AptaPay routes to a single upstream provider, and that provider publishes exactly one API host for live and test traffic alike. No sandbox base URL exists anywhere in its reference documentation. So "test mode" here does not mean what it means on Stripe. It is a **second, real provider account** holding a small real balance, reached over the same wire as production. A test-mode payout moves real money out of a real wallet to a real phone number. It cannot be reversed, because the provider exposes no refund endpoint. | | What you might expect | What actually happens | | --- | --- | --- | | Host | a separate sandbox host | the one production host, always | | Money | simulated | real, in a real wallet | | Recipients | fake numbers accepted | real MSISDNs, really credited | | Undo | reverse the test charge | none — no refund endpoint exists | Two guardrails stand in for the sandbox, and they are permanent, not temporary scaffolding: - **A hard amount ceiling on every test-mode transaction**, enforced by this gateway *before* any provider call. Over it, you get a `422` and no request ever leaves. - **`is_test_mode` stamped on every transaction record**, so a test transaction is identifiable forever after the fact. Mode is a property of **which credentials you hold**, never of a request field — there is no `test: true` to send, and no header that switches it. A live key transacts live; that is the only thing that decides it. See `GET /healthz` for which mode a deployment is running. ## CORS There isn't any, deliberately. This is a server-to-server API and browsers must never call it: signing from client-side JS would put your secret in view-source. Cross-origin browser requests are denied. servers: - url: https://api.pay.aptahq.com description: >- Production. There is no sandbox host, because the upstream provider has none — see "Test mode is NOT a sandbox". Sign the host you dial: the host is part of the canonical string, so a request dialled here must claim `api.pay.aptahq.com`. security: - AptaPaySignature: [] tags: - name: Collections description: Money in. - name: Payouts description: Money out. - name: Refunds description: Reversals — 501 where the routed provider has no refund endpoint. - name: Transactions description: The gateway's own ledger of what it was asked to do. - name: Beneficiaries description: Saved recipients. Stored masked, names re-resolved at payout time. - name: Reference description: Corridors, banks, countries, balances, capability matrix. - name: Float description: Your own claim on the shared wallet pool — what you can actually pay out. - name: FX description: Exchange between your own wallets. Quote is free; exchange moves money. - name: Webhooks description: Provider ingress. Documented for completeness; tenants never call it. - name: Ops description: Health. paths: /v1/fx/exchange: post: tags: - FX summary: Convert between your own wallets — money moves description: > **Actually convert money between two of your own wallets.** The use case is funding a corridor you are short on: you hold UGX, you need to pay out in KES, so you exchange first and then send. Also how a treasury process rebalances float across currencies. To be clear about what this is NOT: it moves money **between your own wallets only**. It never sends money to a customer — that is `POST /v1/payouts`, which handles its own cross-currency conversion via `amount_type`. You do not need to call this before a cross-currency payout. Converts `amount` of `from` into `to` between wallets you already hold. **This moves money**, so `Idempotency-Key` is REQUIRED; a missing one is a 400 and the server never invents one. ONE call. The provider's quote-then-execute handshake happens INTERNALLY and that two-call shape never leaks to you — which is also what keeps the ~60s quote window from being your problem. You do not need to call `/v1/fx/quote` first; that endpoint exists to show a price in a UI. Replaying a completed key returns the original response verbatim with no second conversion. The same key with different parameters is a 422. `rate` in the response is the rate the executed quote encoded — the one actually applied — not a figure recomputed from the returned amounts. **The source wallet must be funded.** The provider prices a conversion it cannot fund but issues no token to execute it, which surfaces here as a 409 `quote_not_executable`. It is terminal: retrying will not help until the wallet holds enough of `from`. `/v1/fx/quote` still returns the rate in that state, so a quote succeeding is not evidence that an exchange will. operationId: exchange parameters: - $ref: '#/components/parameters/IdempotencyKey' requestBody: required: true content: application/json: schema: type: object required: - from - to - amount properties: from: allOf: - $ref: '#/components/schemas/Currency' description: Source currency. Must differ from `to`. to: allOf: - $ref: '#/components/schemas/Currency' description: Destination currency. amount: type: string description: Major units as a decimal STRING. See `/v1/fx/quote`. example: '1000' examples: ugxToKes: summary: Convert 1000 UGX into KES value: from: UGX to: KES amount: '1000' responses: '200': description: The conversion that was applied. content: application/json: schema: $ref: '#/components/schemas/APIResult' example: code: 200 message: OK data: source_currency: UGX source_amount_minor: 1000 destination_currency: KES destination_amount_minor: 3100 rate: 0.031 '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '409': $ref: '#/components/responses/Conflict' '422': $ref: '#/components/responses/Unprocessable' components: parameters: IdempotencyKey: name: Idempotency-Key in: header required: true schema: type: string maxLength: 255 description: | Required. A missing key is a 400 — never a server-generated one. example: laces-order-8f14e45f schemas: Currency: type: string enum: - UGX - RWF - XAF - XOF - KES - GHS - NGN - TZS - ZMW - USD - EUR - GBP APIResult: type: object description: > The single response envelope, used by EVERY endpoint so a consuming app parses one shape everywhere. required: - code - message properties: code: type: integer example: 200 message: type: string example: OK data: description: Present on success. Shape varies per endpoint. error: $ref: '#/components/schemas/GatewayErrorBody' GatewayErrorBody: type: object description: > Machine-readable error classification. EXACTLY ONE of terminal/retriable/ ambiguous is true. laces_api inferred this from the HTTP status and got it wrong, stranding real money twice (2026-08-15, 2026-08-16). Branch on these booleans, never on the status code: terminal -> the provider refused. Reverse the debit and tell the user. retriable -> safe to retry with the SAME Idempotency-Key. ambiguous -> the outcome is UNKNOWN. Do NOT reverse. Poll instead. required: - code - message - terminal - retriable - ambiguous properties: code: type: string description: Stable machine code. Branch on this, never on `message`. example: payout_rejected_by_provider message: type: string description: > Human text from a compiled-in map. NEVER provider text — a stringified provider error can carry an Authorization header. terminal: type: boolean retriable: type: boolean ambiguous: type: boolean details: type: object additionalProperties: type: string responses: BadRequest: description: Validation failed. content: application/json: schema: $ref: '#/components/schemas/APIResult' Unauthorized: description: > Missing, malformed, stale, replayed or invalid signature. Also returned when a body was sent but its raw bytes were unavailable — verified-as-empty must never mean processed-as-full. content: application/json: schema: $ref: '#/components/schemas/APIResult' Conflict: description: '`request_in_progress`, `quote_expired`, or `indeterminate_outcome`.' content: application/json: schema: $ref: '#/components/schemas/APIResult' Unprocessable: description: > Semantically refused BEFORE any provider call — corridor unsupported, amount caps, insufficient float, or an idempotency key reused with different parameters. content: application/json: schema: $ref: '#/components/schemas/APIResult' securitySchemes: AptaPaySignature: type: apiKey in: header name: X-AptaPay-Signature description: > `v1={hex HMAC-SHA256}` over the ten-field canonical string. Sent alongside `X-AptaPay-Key`, `X-AptaPay-Timestamp` and `X-AptaPay-Nonce` — all four are required. OpenAPI can only model one header per scheme, so the other three are described in the Authentication section above. ````