> ## 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 a single line item to an order > Adds a single line item to an order in `draft` or `confirmed` status. Validates that the product is active and belongs to the entity. Runs the pricing engine (qty-break tiers, account pricing level) to compute `sell_rate` if not overridden. Triggers `fullRecalculateOrder` after insert. Idempotent via `Idempotency-Key`. Requires `orders:write` scope. A line cannot be added to a CLOSED AR document: a cancelled/voided order, a posted/fulfilled order (returns `edit_not_allowed` with `suggested_action: create_return`), or a **billed-and-paid / fully-paid order** (`invoice_status` in `paid`/`overdue` or `payment_status` = `paid`; returns `edit_not_allowed` with `suggested_action: revise_order`). To revise a paid order, pass `override: true` in the body with the `orders.revision_override` permission; the edit then proceeds, the order's `revision_count` increments, and the override is recorded in the activity log. The customer must re-acknowledge the new total. ## OpenAPI ````yaml /openapi.yaml post /orders/{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: /orders/{id}/items: parameters: - name: id in: path required: true schema: type: string format: uuid post: tags: - Orders summary: Add a single line item to an order description: > Adds a single line item to an order in `draft` or `confirmed` status. Validates that the product is active and belongs to the entity. Runs the pricing engine (qty-break tiers, account pricing level) to compute `sell_rate` if not overridden. Triggers `fullRecalculateOrder` after insert. Idempotent via `Idempotency-Key`. Requires `orders:write` scope. A line cannot be added to a CLOSED AR document: a cancelled/voided order, a posted/fulfilled order (returns `edit_not_allowed` with `suggested_action: create_return`), or a **billed-and-paid / fully-paid order** (`invoice_status` in `paid`/`overdue` or `payment_status` = `paid`; returns `edit_not_allowed` with `suggested_action: revise_order`). To revise a paid order, pass `override: true` in the body with the `orders.revision_override` permission; the edit then proceeds, the order's `revision_count` increments, and the override is recorded in the activity log. The customer must re-acknowledge the new total. operationId: addOrderItem parameters: - $ref: '#/components/parameters/IdempotencyKey' requestBody: required: true content: application/json: schema: type: object required: - product_id - quantity properties: product_id: type: string format: uuid variant_id: type: string format: uuid quantity: type: integer minimum: 1 sell_rate: type: number description: Override unit price (canonical Arcus field). unit_price: type: number description: >- Alias of sell_rate (Stripe/Shopify convention). Either name accepted. Both with different values returns 400; negative/zero returns 422. When applied price differs from catalog list_price, response carries warnings array entries plus emits order.price_override audit row. list_price: type: number notes: type: string override: type: boolean description: >- Set true (with the orders.revision_override permission) to revise a paid/billed order by adding this line. Without it, a paid/billed order returns 422 edit_not_allowed (suggested_action revise_order). override_reason: type: string description: >- Optional reason recorded in the audit log when override is used. responses: '200': description: >- Added order item. Response includes unit_price alias of sell_rate. When override detected, response also carries warnings array entries (item, code price_override, product_id, catalog_price, applied_price, delta). content: application/json: schema: $ref: '#/components/schemas/OrderItem' '400': $ref: '#/components/responses/Error' '401': $ref: '#/components/responses/Error' '403': $ref: '#/components/responses/Error' '404': $ref: '#/components/responses/Error' '422': $ref: '#/components/responses/Error' 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 schemas: OrderItem: type: object description: A line item on an order. Sub-resource of Order. properties: id: type: string format: uuid entity_id: type: string format: uuid readOnly: true description: > Multi-tenant scoping column (Layer 1 isolation). Set automatically from the parent `orders.entity_id` and enforced by Postgres trigger `trg_order_items_entity_parity` (P0-ENTITY-ID-CHILD-TABLES, 2026-05-18). Cross-tenant writes are rejected at the database layer. order_id: type: string format: uuid product_id: type: string format: uuid nullable: true variant_id: type: string format: uuid nullable: true sku: type: string nullable: true title: type: string quantity: type: integer quantity_fulfilled: type: integer readOnly: true quantity_returned: type: integer readOnly: true sell_rate: type: number description: >- Canonical Arcus per-unit price column (matches order_items.sell_rate). unit_price: type: number description: >- Public-API alias of sell_rate (Stripe/Shopify/QuickBooks convention). Always populated on read; equal to sell_rate. Set per NEW-GAP-API-V1-CALLER-UNIT-PRICE-SILENTLY-OVERRIDDEN 2026-05-17 closure. list_price: type: number pricing_rule_adjustment: type: number readOnly: true description: >- Per-unit pricing-rule savings (list_price minus sell_rate, positive magnitude). Already baked into sell_rate (and therefore line_subtotal) per ASC 606 transaction-price pricing; surfaced for the gross-to-net bridge display, never re-subtracted. coupon_adjustment: type: number readOnly: true description: >- Per-line allocated coupon/order-level discount (signed; negative for a discount). Reflected in line_subtotal. discount_amount: type: number line_subtotal: type: number readOnly: true tax_amount: type: number readOnly: true line_total: type: number readOnly: true adjustments: type: array readOnly: true description: >- Per-line, per-source adjustment breakdown from order_item_adjustments (the canonical SSOT). Each entry attributes a signed line_amount to a source (pricing_rule | order_adjustment | coupon | manual_line_override | return_refund_adjust | restocking_fee). Empty array for lines with no allocations (and on legacy orders predating the writer). Industry parity: Shopify Admin GraphQL LineItem.discountAllocations[]. items: type: object properties: id: type: string format: uuid source_type: type: string description: >- pricing_rule | order_adjustment | coupon | manual_line_override | return_refund_adjust | restocking_fee source_id: type: string format: uuid nullable: true source_label: type: string nullable: true per_unit_amount: type: number nullable: true quantity: type: number line_amount: type: number description: >- Signed per-line adjustment dollar amount (negative for discounts, positive for fees). proration_ratio: type: number nullable: true applied_at: type: string format: date-time nullable: true unit_cost: type: number nullable: true weight: type: number nullable: true is_tax_exempt: type: boolean product_tax_code: type: string nullable: true sort_order: type: integer product_vendor_id: type: string format: uuid nullable: true description: > For `purchase_order` document_type lines only: exact `product_vendors` row this line is bound to (NEW-GAP-ORDER-ITEMS-PRODUCT-VENDOR-ID-PROVENANCE, 2026-05-14). NULL for legacy PO lines and all non-PO doc types; PDF falls back to the deterministic default-vendor-part pick. created_at: type: string format: date-time readOnly: true updated_at: type: string format: date-time readOnly: true 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. ````