> ## 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. # Apply credit memo to an order > Applies the credit memo to an open invoice/order as a payment, through the canonical credit-apply path (same code path as the internal UI): the memo's `balance_remaining` and the account's spendable `credit_balance` decrement, an `order_payments` row is recorded (method `credit`), `order.balance_due` / `payment_status` recalculate, and the GL entry posts (DR Customer Credits liability / CR Accounts Receivable). **Refusal guards:** - 409 `order_already_fully_paid` -- target order has zero open balance. Issue an unapplied customer credit instead, or apply to a different open invoice. - 422 `apply_amount_exceeds_order_balance` -- requested apply amount is greater than the order's current open balance. Reduce the amount and retry. - 400 `credit_memo_not_applicable` -- the memo is voided / expired / fully applied (terminal states are locked). The body includes the memo `status`. - 422 `amount_exceeds_balance_remaining` -- requested apply amount exceeds the credit's `balance_remaining`. - 403 `credit_memo_account_mismatch` -- the memo belongs to a different customer account than the target order. If `amount` is omitted, the full remaining credit is applied (capped at the order's open balance). Industry parity: NetSuite + Acumatica + QuickBooks all refuse credit-to-fully-paid; Arcus matches that behavior. ## OpenAPI ````yaml /openapi.yaml post /customer-credits/{id}/apply 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: /customer-credits/{id}/apply: post: tags: - Accounts Receivable summary: Apply credit memo to an order description: > Applies the credit memo to an open invoice/order as a payment, through the canonical credit-apply path (same code path as the internal UI): the memo's `balance_remaining` and the account's spendable `credit_balance` decrement, an `order_payments` row is recorded (method `credit`), `order.balance_due` / `payment_status` recalculate, and the GL entry posts (DR Customer Credits liability / CR Accounts Receivable). **Refusal guards:** - 409 `order_already_fully_paid` -- target order has zero open balance. Issue an unapplied customer credit instead, or apply to a different open invoice. - 422 `apply_amount_exceeds_order_balance` -- requested apply amount is greater than the order's current open balance. Reduce the amount and retry. - 400 `credit_memo_not_applicable` -- the memo is voided / expired / fully applied (terminal states are locked). The body includes the memo `status`. - 422 `amount_exceeds_balance_remaining` -- requested apply amount exceeds the credit's `balance_remaining`. - 403 `credit_memo_account_mismatch` -- the memo belongs to a different customer account than the target order. If `amount` is omitted, the full remaining credit is applied (capped at the order's open balance). Industry parity: NetSuite + Acumatica + QuickBooks all refuse credit-to-fully-paid; Arcus matches that behavior. operationId: applyCustomerCreditV1 parameters: - name: id in: path required: true schema: type: string format: uuid requestBody: required: true content: application/json: schema: type: object required: - order_id properties: order_id: type: string format: uuid amount: type: number minimum: 0.01 description: >- Must not exceed remaining credit or order open balance. Omit to apply the full remaining credit (capped at the order's open balance). notes: type: string responses: '200': description: Application result content: application/json: schema: type: object properties: credit_memo_id: type: string format: uuid order_id: type: string format: uuid amount_applied: type: number balance_remaining: type: number description: Memo balance remaining after this application. '400': $ref: '#/components/responses/Error' '401': $ref: '#/components/responses/Error' '403': $ref: '#/components/responses/Error' '404': $ref: '#/components/responses/Error' '409': description: > Balance-guard rejection. `code` is `order_already_fully_paid`. The body includes the diagnostic numbers (`current_balance_due`) so the caller can correct and retry. content: application/json: schema: $ref: '#/components/schemas/Error' '422': $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: Error: description: | Alias for ErrorEnvelope. Canonical error response shape used by all API endpoints. Refer to ErrorEnvelope for the full field definition. allOf: - $ref: '#/components/schemas/ErrorEnvelope' 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. ````