> ## 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. # Charge late fees > Charges finance fees on overdue invoices for all eligible customer accounts, or a single account when `account_id` is supplied, posting a late-fee invoice and journal entry for each one; pass `dry_run: true` to preview the calculated amounts without persisting anything. Requires `accounting:write` scope and the entity's `late_fee_enabled` and `late_fee_rate_percent` settings to be configured, and at most one late fee is issued per source invoice per day. ## OpenAPI ````yaml /openapi.yaml post /ar/assess-late-fees 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: /ar/assess-late-fees: post: tags: - Accounting summary: Charge late fees description: >- Charges finance fees on overdue invoices for all eligible customer accounts, or a single account when `account_id` is supplied, posting a late-fee invoice and journal entry for each one; pass `dry_run: true` to preview the calculated amounts without persisting anything. Requires `accounting:write` scope and the entity's `late_fee_enabled` and `late_fee_rate_percent` settings to be configured, and at most one late fee is issued per source invoice per day. operationId: assessLateFeesV1 requestBody: content: application/json: schema: type: object properties: account_id: type: string format: uuid nullable: true description: >- Scope assessment to a single customer account. Omit to assess all eligible accounts. dry_run: type: boolean default: false description: >- Preview mode: calculates fees and returns preview data without persisting any records or posting GL entries. responses: '200': description: Late fee assessment results content: application/json: schema: type: object properties: assessed: type: array description: Invoices that received a finance charge items: type: object properties: source_order_id: type: string format: uuid late_fee_order_id: type: string format: uuid nullable: true description: null when dry_run=true account_id: type: string format: uuid customer_name: type: string invoice_number: type: string balance_due: type: number fee_amount: type: number days_overdue: type: integer compounding: type: string enum: - monthly - daily - none skipped: type: array description: >- Invoices that were evaluated but skipped (exempt, already charged today, min not met, etc.) items: type: object properties: source_order_id: type: string format: uuid account_id: type: string format: uuid reason: type: string total_fee_amount: type: number description: Sum of all fee_amount values in the assessed array dry_run: type: boolean description: >- Reflects the dry_run parameter; true means no records were persisted '401': $ref: '#/components/responses/Error' '403': $ref: '#/components/responses/Error' '422': description: >- Late fees not configured for this entity (late_fee_enabled=false or rate not set) content: application/json: schema: $ref: '#/components/schemas/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: Error: description: | Alias for ErrorEnvelope. Canonical error response shape used by all API endpoints. Refer to ErrorEnvelope for the full field definition. allOf: - $ref: '#/components/schemas/ErrorEnvelope' 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.