> ## 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. # Swap a line item's product in place > Replaces the product on an existing order line in ONE server-side transaction, keeping the captured payment attached so only the price delta needs settling. Composes the canonical add + delete: it adds the replacement line (kit re-explosion, pricing policy, tax) and removes the original (reservation release, kit component cascade) with a single recalculation. `sort_order` is preserved. For channel-sourced orders (Shopify/Amazon/eBay), the replacement line inherits the original line's external line-id triple so revision sync-back can map old -> new. Requires `orders:write` scope. Editing a line on a CLOSED AR document is blocked the same way as update/delete: cancelled/voided or posted/fulfilled (`suggested_action: create_return`, not overridable); paid/billed (`suggested_action: revise_order`). To swap a line on a paid order pass `override: true` with the `orders.revision_override` permission; the swap is audited (`item_swapped`). A kit COMPONENT line returns 422 `kit_component_not_editable` (swap the kit parent). A line with an issued drop-ship PO returns 409 `dropship_po_issued_blocks_line_edit`. ## OpenAPI ````yaml /openapi.yaml post /orders/{id}/items/{item_id}/swap 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/{item_id}/swap: parameters: - name: id in: path required: true schema: type: string format: uuid - name: item_id in: path required: true schema: type: string format: uuid post: tags: - Orders summary: Swap a line item's product in place description: > Replaces the product on an existing order line in ONE server-side transaction, keeping the captured payment attached so only the price delta needs settling. Composes the canonical add + delete: it adds the replacement line (kit re-explosion, pricing policy, tax) and removes the original (reservation release, kit component cascade) with a single recalculation. `sort_order` is preserved. For channel-sourced orders (Shopify/Amazon/eBay), the replacement line inherits the original line's external line-id triple so revision sync-back can map old -> new. Requires `orders:write` scope. Editing a line on a CLOSED AR document is blocked the same way as update/delete: cancelled/voided or posted/fulfilled (`suggested_action: create_return`, not overridable); paid/billed (`suggested_action: revise_order`). To swap a line on a paid order pass `override: true` with the `orders.revision_override` permission; the swap is audited (`item_swapped`). A kit COMPONENT line returns 422 `kit_component_not_editable` (swap the kit parent). A line with an issued drop-ship PO returns 409 `dropship_po_issued_blocks_line_edit`. operationId: swapOrderItem requestBody: required: true content: application/json: schema: type: object required: - product_id properties: product_id: type: string format: uuid description: Replacement product. variant_id: type: string format: uuid description: Replacement variant (required if the product has variants). quantity: type: integer minimum: 1 description: >- Quantity for the replacement line. Defaults to the original line's quantity. sell_rate: type: number description: >- Override unit price for the replacement (canonical Arcus field). unit_price: type: number description: Alias of sell_rate (Stripe/Shopify convention). list_price: type: number notes: type: string override: type: boolean description: >- Set true (with orders.revision_override) to swap a line on a paid/billed order. Without it a paid/billed order returns 422 edit_not_allowed (suggested_action revise_order). override_reason: type: string responses: '200': description: >- Line swapped. Returns old + new order_item ids, quantity, sort_order, and channel_lineage_inherited. content: application/json: schema: type: object properties: old_order_item_id: type: string format: uuid new_order_item_id: type: string format: uuid new_product_id: type: string format: uuid quantity: type: integer sort_order: type: integer channel_lineage_inherited: type: boolean requires_overpayment_review: type: boolean overpayment_amount: type: number nullable: true '400': $ref: '#/components/responses/Error' '401': $ref: '#/components/responses/Error' '403': $ref: '#/components/responses/Error' '404': $ref: '#/components/responses/Error' '409': $ref: '#/components/responses/Error' '422': $ref: '#/components/responses/Error' security: - ApiKeyAuth: [] components: 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. ````