> ## 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 opening on-hand for a (product, variant, location) -- REPLACE semantics, migration-only > NEW-GAP-MIGRATION-PHASE-4-NOT-IDEMPOTENT-P0 (2026-05-18). Canonical REPLACE-NOT-ADD opening-balance writer for one-shot migration loads. Routes to `utils/inventory-helpers.mjs::setOpeningStock`, which sets `inventory_balances.on_hand = target_on_hand` directly (NOT add a delta). Re-running with the same input is a no-op (idempotent); re-running with a different target replaces the prior opening row + FIFO layer + balance. Re-running after the layer has been sold / transferred refuses with 409 `opening_stock_already_consumed`. Scope: **migration:write only**. Live inventory edits MUST use `POST /v1/inventory/adjustments` (delta semantics). GL: NO journal entry posted. Opening Inventory Asset balance lands via `gl_accounts.opening_balance` column write in Phase 5B of the WSS migration. Posting a JE here would double-count. Idempotency: `Idempotency-Key` header honored for double-click protection. Payload-equality short-circuit inside setOpeningStock: a re-run with the same `target_on_hand` + `unit_cost` returns HTTP 200 + `{ idempotent: true, action: 'noop' }` without any DB write. A re-run with a different target returns HTTP 201 + `{ idempotent: false, action: 'replaced' }`. ## 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. 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 opening on-hand for a (product, variant, location) -- REPLACE semantics, migration-only description: | NEW-GAP-MIGRATION-PHASE-4-NOT-IDEMPOTENT-P0 (2026-05-18). Canonical REPLACE-NOT-ADD opening-balance writer for one-shot migration loads. Routes to `utils/inventory-helpers.mjs::setOpeningStock`, which sets `inventory_balances.on_hand = target_on_hand` directly (NOT add a delta). Re-running with the same input is a no-op (idempotent); re-running with a different target replaces the prior opening row + FIFO layer + balance. Re-running after the layer has been sold / transferred refuses with 409 `opening_stock_already_consumed`. Scope: **migration:write only**. Live inventory edits MUST use `POST /v1/inventory/adjustments` (delta semantics). GL: NO journal entry posted. Opening Inventory Asset balance lands via `gl_accounts.opening_balance` column write in Phase 5B of the WSS migration. Posting a JE here would double-count. Idempotency: `Idempotency-Key` header honored for double-click protection. Payload-equality short-circuit inside setOpeningStock: a re-run with the same `target_on_hand` + `unit_cost` returns HTTP 200 + `{ idempotent: true, action: 'noop' }` without any DB write. A re-run with a different target returns HTTP 201 + `{ idempotent: false, action: 'replaced' }`. 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. ````