> ## 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 > Reduces the credit memo balance and reduces order.balance_due by the specified amount. Posts a GL entry (DR Customer Escrow / CR AR) to net the credit against the receivable. **Balance 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. - `apply_amount_exceeds_order_balance` -- requested apply amount is greater than the order's current open balance. Reduce the amount and retry. - `credit_voided` -- source credit memo is voided. - `insufficient_credit_balance` -- requested apply amount exceeds the credit's `balance_remaining`. Industry parity: NetSuite + Acumatica + QuickBooks all refuse credit-to-fully-paid; Arcus matches that behavior. Phase 2 (separate PENDING) will auto-route overflow into an unapplied customer credit. ## 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: > Reduces the credit memo balance and reduces order.balance_due by the specified amount. Posts a GL entry (DR Customer Escrow / CR AR) to net the credit against the receivable. **Balance 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. - `apply_amount_exceeds_order_balance` -- requested apply amount is greater than the order's current open balance. Reduce the amount and retry. - `credit_voided` -- source credit memo is voided. - `insufficient_credit_balance` -- requested apply amount exceeds the credit's `balance_remaining`. Industry parity: NetSuite + Acumatica + QuickBooks all refuse credit-to-fully-paid; Arcus matches that behavior. Phase 2 (separate PENDING) will auto-route overflow into an unapplied customer credit. 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 - amount properties: order_id: type: string format: uuid amount: type: number minimum: 0.01 description: Must not exceed remaining credit or order open balance. responses: '200': description: Updated credit memo after application content: application/json: schema: $ref: '#/components/schemas/CustomerCredit' '401': $ref: '#/components/responses/Error' '403': $ref: '#/components/responses/Error' '409': description: > Balance-guard rejection. `code` is one of `order_already_fully_paid`, `apply_amount_exceeds_order_balance`, `credit_voided`, `insufficient_credit_balance`. The body includes the diagnostic numbers (`current_balance_due`, `apply_amount`) so the caller can correct and retry. content: application/json: schema: $ref: '#/components/schemas/Error' '422': $ref: '#/components/responses/Error' security: - ApiKeyAuth: [] components: schemas: CustomerCredit: type: object description: > A customer credit memo representing a future payment obligation by Arcus to an account. Tracks open_balance for partial application across multiple orders. GL: DR AR Clearing / CR AR on creation; DR AR / CR Cash on application. properties: id: type: string format: uuid readOnly: true entity_id: type: string format: uuid readOnly: true account_id: type: string format: uuid description: The customer account this credit belongs to. amount: type: number description: Original credit amount issued. open_balance: type: number readOnly: true description: Remaining unapplied balance. status: type: string enum: - open - partially_applied - fully_applied - voided readOnly: true reason: type: string nullable: true memo: type: string nullable: true gl_account_id: type: string format: uuid nullable: true description: Clearing account used for this credit. journal_entry_id: type: string format: uuid nullable: true readOnly: true description: The GL entry that created this credit. created_at: type: string format: date-time readOnly: true updated_at: type: string format: date-time readOnly: true voided_at: type: string format: date-time nullable: true readOnly: true 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 responses: Error: description: Error response (400/401/403/404/409/422/429/500) content: application/json: schema: $ref: '#/components/schemas/ErrorEnvelope' 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. ````