> ## Documentation Index > Fetch the complete documentation index at: https://docs.arcuserp.com/llms.txt > Use this file to discover all available pages before exploring further. # Create exchange rate (NOT IMPLEMENTED) > **NOTICE: Multi-currency support is NOT implemented in Arcus.** This endpoint accepts writes for forward-compatibility but exchange rate data has no business effect on any transaction. Returns HTTP 501 unless `entities.settings.multi_currency_enabled` is true (which no entity has set, as of 2026-05-22). Append-only per-day FX snapshots. Currency fields accept either a **UUID** (from the currencies resource) or an **ISO-4217 code** (e.g. "USD", "EUR", "GBP"). Codes are resolved to UUIDs at write time; UUIDs are canonical in the database (Rule 23 SSOT). If both `from_currency` and `from_currency_id` are provided, `from_currency_id` takes precedence. `effective_date` is accepted as an alias for `as_of_date`. ## OpenAPI ````yaml /openapi.yaml post /exchange-rates openapi: 3.1.0 info: title: Arcus ERP Public API version: 1.0.0 description: > Arcus ERP public REST API. Designed for external integrations and data migration. **Authentication.** Bearer token (API key) via the `Authorization` header. Format: `Authorization: Bearer ark_live_ent__` (or `ark_test_*` for sandbox). API keys are issued per-entity in **Settings > Developers > API Keys**. **Entity scoping.** The entity is encoded in the API key prefix; routes are flat (e.g. `/v1/accounts`, `/v1/orders`, `/v1/products`). A small set of platform endpoints (migration, reconciliation, events, webhook endpoints, API keys) use the `/v1/entities/{entity_id}/...` form -- those are noted in their tags. **Key capabilities.** - Related-resource hydration via `?expand[]=` (see `x-arcus-expand` on each resource). - Cursor-based pagination (`starting_after` / `ending_before` / `limit`). - Idempotency via the `Idempotency-Key` header. - Webhook events for asynchronous notification. - Conditional requests / ETag for cache validation. servers: - url: https://api.arcuserp.com/v1 description: Arcus ERP API (accepts both live `ark_live_*` and test `ark_test_*` keys) - url: https://dev-api.arcuserp.com/v1 description: >- Dev sandbox API (test-only data, accepts `ark_test_*` keys against dev RDS) security: [] paths: /exchange-rates: post: tags: - Masters summary: Create exchange rate (NOT IMPLEMENTED) description: > **NOTICE: Multi-currency support is NOT implemented in Arcus.** This endpoint accepts writes for forward-compatibility but exchange rate data has no business effect on any transaction. Returns HTTP 501 unless `entities.settings.multi_currency_enabled` is true (which no entity has set, as of 2026-05-22). Append-only per-day FX snapshots. Currency fields accept either a **UUID** (from the currencies resource) or an **ISO-4217 code** (e.g. "USD", "EUR", "GBP"). Codes are resolved to UUIDs at write time; UUIDs are canonical in the database (Rule 23 SSOT). If both `from_currency` and `from_currency_id` are provided, `from_currency_id` takes precedence. `effective_date` is accepted as an alias for `as_of_date`. operationId: createExchangeRate parameters: - name: Idempotency-Key in: header required: false schema: type: string requestBody: required: true content: application/json: schema: type: object required: - rate properties: from_currency: description: >- ISO-4217 currency code OR UUID of the source currency. Alias: resolved to from_currency_id. anyOf: - type: string pattern: ^[A-Z]{3}$ example: USD description: ISO-4217 code - type: string format: uuid description: currencies resource UUID from_currency_id: type: string format: uuid description: >- UUID of the source currency (canonical form). Overrides from_currency if both provided. to_currency: description: >- ISO-4217 currency code OR UUID of the target currency. Alias: resolved to to_currency_id. anyOf: - type: string pattern: ^[A-Z]{3}$ example: GBP description: ISO-4217 code - type: string format: uuid description: currencies resource UUID to_currency_id: type: string format: uuid description: >- UUID of the target currency (canonical form). Overrides to_currency if both provided. rate: type: number description: >- Exchange rate (units of to_currency per 1 unit of from_currency) as_of_date: type: string format: date description: 'Date this rate applies to. Alias: effective_date.' effective_date: type: string format: date description: >- Alias for as_of_date. Accepted if as_of_date is not provided. source: type: string description: Rate source identifier (e.g. ecb manual: null fixer.io): null external_source: type: string external_id: type: string metadata: type: object responses: '201': description: Created exchange rate content: application/json: schema: type: object '400': $ref: '#/components/responses/Error' '401': $ref: '#/components/responses/Error' '403': $ref: '#/components/responses/Error' '409': $ref: '#/components/responses/Error' security: - ApiKeyAuth: [] components: responses: Error: description: Error response (400/401/403/404/409/422/429/500) content: application/json: schema: $ref: '#/components/schemas/ErrorEnvelope' schemas: ErrorEnvelope: type: object description: | Canonical error response envelope. All API errors use this shape. required: - error - code properties: error: type: string description: Machine-readable error key example: not_found code: type: string description: Machine-readable error code (often same as error) example: not_found type: type: string enum: - validation_error - permission_error - not_found - conflict - rate_limit - internal - expand_error - not_implemented example: not_found hint: type: string description: Human-readable one-sentence explanation (English) example: >- The requested order does not exist or does not belong to this entity. param: type: string description: The parameter that caused the error, if applicable example: expand[0] required: type: string description: The scope required (only on insufficient_scope errors) example: accounts:read request_id: type: string description: >- Unique request ID for support tracing (maps to CloudWatch log stream) example: req_abc123 securitySchemes: ApiKeyAuth: type: http scheme: bearer description: | API key issued per entity via Settings > Developers > API Keys. Each key carries scopes (e.g. orders:read, products:write). Bearer token format: Authorization: Bearer ark_live_ent__ Test keys use ark_test_ent__. Both are issued per entity via Settings > Developers > API Keys. ````