> ## 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. # Update a line item > Updates a line item's quantity, price, discount, tax rate, or notes and recalculates the order's totals. Editing a line on a cancelled, fulfilled, or fully paid order is blocked unless the caller passes `override: true` with the required permission, and a line whose drop-ship purchase order has already been issued cannot have its quantity or vendor changed directly. ## OpenAPI ````yaml /openapi.yaml patch /orders/{id}/items/{item_id} 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. **Changelog.** Entries are dated and name every published contract whose MEANING moved, not only the ones whose field names changed. The narrative version of the same entries, written for integrators, is published at https://arcuserp.mintlify.app/changelog. **2026-09-22 (planned 2026-09-21), REORDER-BUYER-TRUTH: demand changed what it MEANS on three published contracts, with no field renamed.** An integrator that pins field names sees no breakage and different numbers, which is why this entry exists. - **Demand now counts build consumption.** `demand_avg_per_day` on the public product, kit and inventory-balance objects, and `daily_demand` / `demand_basis` / `net_suggested_qty` on `GET /v1/purchasing/reorder-report`, are composed from fulfilled sales lines PLUS posted `build_consume` inventory draws: each physical decrement of a product counts exactly once. The previous rule adopted an internal-consumption basis only when the sales blend was exactly zero, so a product both sold AND consumed into work orders planned as if the build draws did not exist. Products drawn into work orders move; on one production-shaped dataset five did, the largest from 0.05/day to 14.95/day. - **`demand_basis` now carries four values, not two:** `sales`, `sales_and_builds`, `builds` and `consumption`. A consumer with a two-branch reader (anything that is not `consumption` is `sales`) silently hides the two new ones. - **`current_demand_units` on `GET /v1/inventory/balances/:id` moved, by a second rule.** It counts committed-but-unshipped CUSTOMER demand, and it now counts a kit component's own line rather than its parent kit line, and excludes non-sales documents. On one production dataset 269 of 1,043 balance rows changed, 227 of them downward; the largest single move was 1,941 to 25, on a product whose open PURCHASE order line had been reported as customer demand. Re-baseline anything that alerts or reorders off this field. - `run_rate_30/90/180/365` and `blended_daily` on the same balance object move for the first reason above. - **Added, not changed:** `GET /v1/purchasing/reorder-report` accepts `demand_window` and returns the unit, cover-through and reorder-point-provenance fields documented on that operation; `order_multiple` is accepted and returned on the product-vendor doors. - **Volume note.** The `inventory.low_stock`, `inventory.out_of_stock` and `inventory.back_in_stock` webhook events are population-gated on `on_hand <= reorder_point`, and reorder points move with the demand above, so subscribers should expect a one-time step change in event volume around the release. 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/{item_id}: parameters: - name: id in: path required: true schema: type: string format: uuid - name: item_id in: path required: true schema: type: string format: uuid patch: tags: - Orders summary: Update a line item description: >- Updates a line item's quantity, price, discount, tax rate, or notes and recalculates the order's totals. Editing a line on a cancelled, fulfilled, or fully paid order is blocked unless the caller passes `override: true` with the required permission, and a line whose drop-ship purchase order has already been issued cannot have its quantity or vendor changed directly. operationId: updateOrderItem parameters: - $ref: '#/components/parameters/IdempotencyKey' requestBody: required: true content: application/json: schema: type: object properties: 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). Conflict / invalid handled identically to add. Triggers warnings entries plus order.price_override audit when applied price differs from catalog. notes: type: string override: type: boolean description: >- Set true (with the orders.revision_override permission) to revise a paid/billed order. 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: >- Updated order item. Response includes unit_price alias. When override detected, response carries warnings array entries. 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 received_floor: type: number readOnly: true description: > PURCHASE-ORDER lines only. The lowest quantity this line may be reduced to: the SAFEST of the line's `quantity_fulfilled` and its receipted-plus-damaged total, clamped at 0. The two sources disagree on migrated rows and on rows whose receipt was undone, so the maximum of both is used -- it can only ever refuse a reduction that either source forbids. line_editability: allOf: - $ref: '#/components/schemas/PoLineEditability' readOnly: true description: > PURCHASE-ORDER lines only. Per-field verdicts from the same predicate the write handlers enforce, so a client never has to restate the stage rules. 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 PoLineEditability: type: object description: > Per-LINE editability, projected on every item of a purchase order (PO-LINE-EDIT-2026-08-17). The server remains the hard gate; this exists so a client renders the same verdict the write handler will enforce, with a reason, instead of restating the stage rules. properties: qty: allOf: - $ref: '#/components/schemas/PoFieldVerdict' - type: object properties: floor: type: number description: > The lowest quantity this line may be reduced to -- the SAFEST of the line's `quantity_fulfilled` and its receipted-plus-damaged total. Clamped at 0. unit_cost: allOf: - $ref: '#/components/schemas/PoFieldVerdict' - type: object properties: warn_received_qty: type: number description: > Units already received against this line. Cost edits stay ALLOWED after a receipt (the receipt stamped its own cost, so inventory and the FIFO layers are unaffected); this count is the warning that the three-way-match baseline and the bill's intent-vs-billed panel will move. delete: $ref: '#/components/schemas/PoFieldVerdict' notes: $ref: '#/components/schemas/PoFieldVerdict' 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 PoFieldVerdict: type: object description: A single per-field editability verdict. properties: allowed: type: boolean reason: type: string nullable: true enum: - po_pending_approval_edit_locked - po_pending_approval_and_terminal - po_status_locked - po_status_unknown_locked - line_has_receipts - delete_blocked_on_processing - qty_below_received - notes_only_on_terminal description: > NULL when allowed. Otherwise a stable token; the client renders the prose. `po_status_unknown_locked` is the fail-closed answer for an order in a status the predicate has not ruled on, and is deliberately DISTINCT from `po_status_locked` so "we lock this on purpose" and "nobody has ruled on this" are never indistinguishable. 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. ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.