> ## 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.

# Edit a purchase order line item in place

> Edits an existing purchase-order line's `quantity`, `unit_cost`, and/or
`notes` IN PLACE -- instead of deleting and re-adding the line. This
preserves the line's `order_item.id` continuity (the FK target of any
receipt history), the PO `revision_count` semantics, the per-line
activity trail, and the 3-way-match baseline.

Editable fields are `quantity`, `unit_cost`, and `notes` only. To change
which product a line is for, delete the line and add a new one
(a product swap is a different line, not an edit).

Eligibility:

- 422 `po_pending_approval_edit_locked` if the PO is awaiting approval.
- 422 `po_status_locked` if the PO is `cancelled`, `fulfilled`,
  `archived`, or `expired`.
- 422 `qty_below_received` if the new `quantity` is below the quantity
  already received against the line (the body carries `received_total`,
  `requested_qty`, and a `hint`).

Side effects (THE ONE RULE -- same canonical handler as the in-app edit):
adjusts the `on_purchase_order` cache by the net unreceived-quantity
delta, recomputes the PO header total, bumps `revision_count` on a sent
PO when a vendor-visible field (`quantity` or `unit_cost`) changes,
emits `purchase_order.updated` + `purchase_order_line.updated` (and
`purchase_order.revised` when revised) broadcasts (Rule 13), and writes a
`po_line_updated` activity entry with the changed fields and prior values
(Rule 20).

<Note>Required API key scope: `purchasing:write`</Note>




## OpenAPI

````yaml /openapi.yaml patch /purchase-orders/{id}/items/{itemId}
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_<code>_<random>` (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:
  /purchase-orders/{id}/items/{itemId}:
    parameters:
      - name: id
        in: path
        required: true
        schema:
          type: string
          format: uuid
        description: The purchase order id.
      - name: itemId
        in: path
        required: true
        schema:
          type: string
          format: uuid
        description: The PO line item (order_item) id to edit.
    patch:
      tags:
        - Purchasing
      summary: Edit a purchase order line item in place
      description: >
        Edits an existing purchase-order line's `quantity`, `unit_cost`, and/or

        `notes` IN PLACE -- instead of deleting and re-adding the line. This

        preserves the line's `order_item.id` continuity (the FK target of any

        receipt history), the PO `revision_count` semantics, the per-line

        activity trail, and the 3-way-match baseline.


        Editable fields are `quantity`, `unit_cost`, and `notes` only. To change

        which product a line is for, delete the line and add a new one

        (a product swap is a different line, not an edit).


        Eligibility:


        - 422 `po_pending_approval_edit_locked` if the PO is awaiting approval.

        - 422 `po_status_locked` if the PO is `cancelled`, `fulfilled`,
          `archived`, or `expired`.
        - 422 `qty_below_received` if the new `quantity` is below the quantity
          already received against the line (the body carries `received_total`,
          `requested_qty`, and a `hint`).

        Side effects (THE ONE RULE -- same canonical handler as the in-app
        edit):

        adjusts the `on_purchase_order` cache by the net unreceived-quantity

        delta, recomputes the PO header total, bumps `revision_count` on a sent

        PO when a vendor-visible field (`quantity` or `unit_cost`) changes,

        emits `purchase_order.updated` + `purchase_order_line.updated` (and

        `purchase_order.revised` when revised) broadcasts (Rule 13), and writes
        a

        `po_line_updated` activity entry with the changed fields and prior
        values

        (Rule 20).


        <Note>Required API key scope: `purchasing:write`</Note>
      operationId: updatePurchaseOrderItemV1
      parameters:
        - name: Idempotency-Key
          in: header
          required: false
          schema:
            type: string
            maxLength: 255
          description: Optional idempotency key for safe retries (Stripe-style).
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              minProperties: 1
              properties:
                quantity:
                  type: integer
                  minimum: 1
                  description: >-
                    New quantity ordered. Must be a positive integer and >= the
                    quantity already received.
                unit_cost:
                  type: number
                  minimum: 0
                  description: >-
                    New unit cost. Mirrored onto the line's sell rate / list
                    price and re-totals the line.
                notes:
                  type: string
                  nullable: true
                  description: >-
                    Per-line internal note (vendor-internal; does not bump the
                    PO revision).
      responses:
        '200':
          description: >-
            Line item updated. Returns the updated line plus the new
            `revision_count` (null on a draft / unsent PO).
          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':
          description: >
            Edit refused. One of: `po_pending_approval_edit_locked` (awaiting

            approval), `po_status_locked`
            (cancelled/fulfilled/archived/expired),

            or `qty_below_received` (new quantity below already-received total).
          content:
            application/json:
              schema:
                $ref: '#/components/responses/Error'
      security:
        - ApiKeyAuth: []
components:
  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_<code>_<random>
        Test keys use ark_test_ent_<code>_<random>. Both are issued per entity
        via Settings > Developers > API Keys.

````