> ## 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. # Which invoices a posted customer receipt pays > The per-invoice breakdown behind a multi-invoice customer receipt: which invoices it was applied to, how much each one received from THIS receipt, what each one still owes afterwards, and how much of each invoice was settled by some OTHER receipt (applied_elsewhere). This is the read half of the pair. It is the SAME reader the staff AR Payments tab expands a receipt row with and the same one the Change applied invoices dialog edits, so an integration and the screen can never disagree about how a customer's cash was attributed. Read-only. Entity-scoped: a receipt id outside the calling key's entity answers 404, never an empty list. ## OpenAPI ````yaml /openapi.yaml get /customer-payments/{id}/applications 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: /customer-payments/{id}/applications: get: tags: - Payments summary: Which invoices a posted customer receipt pays description: > The per-invoice breakdown behind a multi-invoice customer receipt: which invoices it was applied to, how much each one received from THIS receipt, what each one still owes afterwards, and how much of each invoice was settled by some OTHER receipt (applied_elsewhere). This is the read half of the pair. It is the SAME reader the staff AR Payments tab expands a receipt row with and the same one the Change applied invoices dialog edits, so an integration and the screen can never disagree about how a customer's cash was attributed. Read-only. Entity-scoped: a receipt id outside the calling key's entity answers 404, never an empty list. operationId: getCustomerPaymentApplications parameters: - name: id in: path required: true schema: type: string format: uuid description: The order_payments id of the receipt. responses: '200': description: The receipt and its per-invoice applications content: application/json: schema: type: object properties: data: type: object properties: payment_id: type: string format: uuid receipt_amount: type: number payment_method: type: string status: type: string posted_at: type: string format: date-time journal_entry_id: type: string format: uuid nullable: true applications_total: type: number description: > Sum of amount_applied across the rows below. Equals receipt_amount unless part of the receipt was held as a credit on account. applications: type: array items: type: object properties: application_id: type: string format: uuid order_id: type: string format: uuid document_number: type: string description: >- The invoice number, or the order number when the document carries none. order_number: type: string invoice_number: type: string nullable: true document_date: type: string format: date due_date: type: string format: date nullable: true amount_applied: type: number description: What THIS receipt put on this invoice. order_total: type: number amount_paid: type: number balance_due: type: number description: >- What the invoice still owes after every application, including this one. applied_elsewhere: type: number description: >- What OTHER receipts have applied to the same invoice. payment_status: type: string invoice_status: type: string nullable: true '400': $ref: '#/components/responses/Error' '401': $ref: '#/components/responses/Error' '403': $ref: '#/components/responses/Error' '404': $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. ````