> ## 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. # Add line items to an RMA > Adds one or more items to a draft or authorized RMA. Each item must reference a valid `order_item_id` from the original order. Validates that the return quantity does not exceed the original ordered quantity minus already-returned quantity (accounting for any existing open RMAs against the same line). Returns 422 `qty_exceeds_remaining` on overage. Requires `returns:write` scope. ## OpenAPI ````yaml /openapi.yaml post /returns/{id}/items 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: /returns/{id}/items: parameters: - name: id in: path required: true schema: type: string format: uuid post: tags: - Returns summary: Add line items to an RMA description: > Adds one or more items to a draft or authorized RMA. Each item must reference a valid `order_item_id` from the original order. Validates that the return quantity does not exceed the original ordered quantity minus already-returned quantity (accounting for any existing open RMAs against the same line). Returns 422 `qty_exceeds_remaining` on overage. Requires `returns:write` scope. operationId: addReturnItems parameters: - $ref: '#/components/parameters/IdempotencyKey' requestBody: required: true content: application/json: schema: type: object required: - items properties: items: type: array items: type: object required: - order_item_id - quantity_authorized properties: order_item_id: type: string format: uuid quantity_authorized: type: integer minimum: 1 reason_code: type: string enum: - defective - damaged_in_transit - wrong_item_shipped - not_as_described - no_longer_needed - found_better_price - arrived_late - other - unspecified description: >- Per-line return reason. Powers returns-by-reason analytics (R31). Defaults to 'unspecified' if omitted (NEW-GAP-DATA-ANALYTICS-OPERATIONAL-WIRING 2026-05-16). responses: '200': description: Items added '400': $ref: '#/components/responses/Error' '401': $ref: '#/components/responses/Error' '403': $ref: '#/components/responses/Error' '404': $ref: '#/components/responses/Error' '422': description: >- Quantity exceeds remaining. Error code `qty_exceeds_remaining` with fields `order_item_id`, `requested`, `remaining`, `sold`, `prior`. content: application/json: schema: type: object properties: code: type: string example: qty_exceeds_remaining order_item_id: type: string format: uuid requested: type: integer remaining: type: integer sold: type: integer prior: type: integer security: - ApiKeyAuth: [] components: parameters: IdempotencyKey: name: Idempotency-Key in: header required: false description: | Client-generated unique key for idempotent POST/PATCH/DELETE operations. Alias for the Idempotency parameter. Max 255 chars. On retry with the same key, the original response is returned without re-executing the operation. Keys expire after 24 hours. schema: type: string maxLength: 255 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. ````