> ## 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. # Set an opening inventory balance > Sets a product's opening on-hand quantity and unit cost at a location to an exact target value rather than adding a delta, for one-time migration loads only; requires `migration:write` scope. Re-running with the same target is a no-op, but re-running after the opening quantity has already been sold or transferred returns a 409. ## OpenAPI ````yaml /openapi.yaml post /inventory/opening-stock 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: /inventory/opening-stock: post: tags: - Inventory - Migration summary: Set an opening inventory balance description: >- Sets a product's opening on-hand quantity and unit cost at a location to an exact target value rather than adding a delta, for one-time migration loads only; requires `migration:write` scope. Re-running with the same target is a no-op, but re-running after the opening quantity has already been sold or transferred returns a 409. operationId: postInventoryOpeningStock parameters: - $ref: '#/components/parameters/IdempotencyKey' requestBody: required: true content: application/json: schema: type: object required: - product_id - location_id - target_on_hand properties: product_id: type: string format: uuid description: Arcus product UUID. location_id: type: string format: uuid description: Arcus location UUID. variant_id: type: string format: uuid nullable: true description: >- Optional product_variants UUID; null for non-variant products. target_on_hand: type: integer minimum: 0 description: > The TARGET on-hand value (not a delta). setOpeningStock writes `inventory_balances.on_hand = target_on_hand` directly. unit_cost: type: number format: float minimum: 0.0001 description: > Per-unit cost. Required when target_on_hand > 0; ignored when target_on_hand = 0. setOpeningStock refuses positive opening qty without a positive unit_cost (would corrupt FIFO + GL opening Inventory Asset balance). external_id: type: string maxLength: 80 description: > Optional source-system row identifier (e.g., Versa snapshot id). Stored on `inventory_transactions.reference_number` for audit traceability. Idempotency keys on (entity, product, location, reference_type='opening_balance'), NOT on external_id; external_id is informational only. notes: type: string description: >- Optional free-text source memo. Stored on `inventory_transactions.notes`. examples: fresh_opening: summary: Fresh opening stock (no prior opening row) value: product_id: 7f6f3e14-eaad-4c45-b922-209f6dc6d140 location_id: 91aa7588-4dc7-4edd-b172-7de91f5e1f78 target_on_hand: 144 unit_cost: 44 external_id: VERSA-SNAPSHOT-99127 notes: Opening stock from Versa snapshot (Dayton facility) idempotent_rerun: summary: Re-run with same target (idempotent no-op) description: | Identical payload to a prior call. Returns HTTP 200 + { idempotent: true, action: 'noop' }. No DB writes. value: product_id: 7f6f3e14-eaad-4c45-b922-209f6dc6d140 location_id: 91aa7588-4dc7-4edd-b172-7de91f5e1f78 target_on_hand: 144 unit_cost: 44 external_id: VERSA-SNAPSHOT-99127 responses: '200': description: | Idempotent no-op. A prior opening row exists at this (entity, product, variant, location) with the same target_on_hand and unit_cost. No DB write occurred. Returns the existing balance + transaction. content: application/json: schema: type: object properties: object: type: string enum: - inventory_opening_stock_result action: type: string enum: - noop idempotent: type: boolean balance: type: object transaction: type: object fifo_layer: type: object nullable: true '201': description: | Created (no prior opening row) OR replaced (prior opening row with different target). The opening txn + FIFO layer + balance now reflect target_on_hand exactly. content: application/json: schema: type: object properties: object: type: string enum: - inventory_opening_stock_result action: type: string enum: - created - replaced idempotent: type: boolean balance: type: object transaction: type: object fifo_layer: type: object nullable: true '400': $ref: '#/components/responses/Error' '401': $ref: '#/components/responses/Error' '403': $ref: '#/components/responses/Error' '409': description: | Opening stock at this (entity, product, variant, location) has already been consumed (sold / transferred). setOpeningStock refuses to mutate a layer that's no longer the live opening. Reconcile via POST /v1/inventory/adjustments deltas instead. content: application/json: schema: type: object properties: error: type: string enum: - opening_stock_already_consumed code: type: string enum: - opening_stock_already_consumed hint: type: string consumed_qty: type: integer opening_qty: type: integer 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 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. ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.