Edit a purchase order line item in place

Drop-ship linked line (2026-07-10): a quantity INCREASE on a line linked to a sales order (drop-ship) is capped at received_total + the linked SO open demand and returns 422 dropship_po_qty_exceeds_so_open beyond it; decreases keep the received-quantity floor only.

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).

Required API key scope: purchasing:write

PATCH /purchase-orders/{id}/items/{itemId}

Edit a purchase order line item in place

cURL

curl --request PATCH \
  --url https://api.arcuserp.com/v1/purchase-orders/{id}/items/{itemId} \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "quantity": 2,
  "unit_cost": 1,
  "notes": "<string>"
}
'

200

{
  "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "entity_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "order_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "product_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "variant_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "sku": "<string>",
  "title": "<string>",
  "quantity": 123,
  "quantity_fulfilled": 123,
  "quantity_returned": 123,
  "received_floor": 123,
  "line_editability": {
    "qty": {
      "allowed": true,
      "reason": "po_pending_approval_edit_locked",
      "floor": 123
    },
    "unit_cost": {
      "allowed": true,
      "reason": "po_pending_approval_edit_locked",
      "warn_received_qty": 123
    },
    "delete": {
      "allowed": true,
      "reason": "po_pending_approval_edit_locked"
    },
    "notes": {
      "allowed": true,
      "reason": "po_pending_approval_edit_locked"
    }
  },
  "sell_rate": 123,
  "unit_price": 123,
  "list_price": 123,
  "pricing_rule_adjustment": 123,
  "coupon_adjustment": 123,
  "discount_amount": 123,
  "line_subtotal": 123,
  "tax_amount": 123,
  "line_total": 123,
  "adjustments": [
    {
      "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
      "source_type": "<string>",
      "source_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
      "source_label": "<string>",
      "per_unit_amount": 123,
      "quantity": 123,
      "line_amount": 123,
      "proration_ratio": 123,
      "applied_at": "2023-11-07T05:31:56Z"
    }
  ],
  "unit_cost": 123,
  "weight": 123,
  "is_tax_exempt": true,
  "product_tax_code": "<string>",
  "sort_order": 123,
  "product_vendor_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "created_at": "2023-11-07T05:31:56Z",
  "updated_at": "2023-11-07T05:31:56Z"
}

Authorizations

Authorization · string · header · required

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.

Headers

Idempotency-Key · string

Optional idempotency key for safe retries (Stripe-style).

Maximum string length: 255

Path Parameters

id · string<uuid> · required

The purchase order id.

itemId · string<uuid> · required

The PO line item (order_item) id to edit.

Body

application/json

quantity · integer

New quantity ordered. Must be a positive integer and >= the quantity already received.

Required range: x >= 1

unit_cost · number

New unit cost. Mirrored onto the line's sell rate / list price and re-totals the line.

Required range: x >= 0

notes · string | null

Per-line internal note (vendor-internal; does not bump the PO revision).

Response

200

application/json

Line item updated. Returns the updated line plus the new revision_count (null on a draft / unsent PO).

A line item on an order. Sub-resource of Order.

id · string<uuid>

entity_id · string<uuid> · read-only

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 · string<uuid>

product_id · string<uuid> | null

variant_id · string<uuid> | null

sku · string | null

title · string

quantity · integer

quantity_fulfilled · integer · read-only

quantity_returned · integer · read-only

received_floor · number · read-only

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 · object

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.

Show child attributes

sell_rate · number

Canonical Arcus per-unit price column (matches order_items.sell_rate).

unit_price · number

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 · number

pricing_rule_adjustment · number · read-only

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 · number · read-only

Per-line allocated coupon/order-level discount (signed; negative for a discount). Reflected in line_subtotal.

discount_amount · number

line_subtotal · number · read-only

tax_amount · number · read-only

line_total · number · read-only

adjustments · object[] · read-only

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[].

Show child attributes

unit_cost · number | null

weight · number | null

is_tax_exempt · boolean

product_tax_code · string | null

sort_order · integer

product_vendor_id · string<uuid> | null

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 · string<date-time> · read-only

updated_at · string<date-time> · read-only