> ## Documentation Index > Fetch the complete documentation index at: https://docs.contazen.ro/llms.txt > Use this file to discover all available pages before exploring further. # Estimate Payment Date > Predict when an unpaid invoice is likely to be paid, based on client history ## OpenAPI ````yaml GET /invoices/{id}/payment-estimate openapi: 3.1.0 info: title: Contazen API version: 1.2.0 description: > Build powerful integrations with the Contazen invoicing platform. The Contazen API is organized around REST, has predictable resource-oriented URLs, accepts JSON request bodies, returns JSON-encoded responses, and uses standard HTTP response codes, authentication, and verbs. ## Authentication The API uses Bearer token authentication. Include your API key in the Authorization header. ### Getting your API Key 1. Log in to your Contazen account 2. Navigate to Settings > API 3. Generate or copy your API key (starts with `sk_live_` for production or `sk_test_` for testing) ### Using the API Key Include your API key in the Authorization header: ``` Authorization: Bearer sk_live_YOUR_API_KEY ``` ### Example Request with cURL ```bash curl --request GET \ --url https://api.contazen.ro/v1/clients \ --header 'Authorization: Bearer sk_live_YOUR_API_KEY' \ --header 'Accept: application/json' ``` ## Rate Limiting - 1000 requests per hour per API key - 100 create operations per minute per API key Rate limit information is included in response headers: - `X-RateLimit-Limit`: Maximum requests allowed - `X-RateLimit-Remaining`: Requests remaining - `X-RateLimit-Reset`: Reset time (Unix timestamp) ## Pagination All list endpoints return paginated results with the following format: ```json { "success": true, "data": { "object": "list", "data": [...], "has_more": true, "total": 245, "page": 1, "per_page": 50, "total_pages": 5 }, "meta": { "version": "v1", "request_id": "req_1a2b3c4d", "response_time": "23.45ms" } } ``` ## Multi-Work-Point Access API keys belong to a specific work point but can access data from all work points within the same parent company. ## Error Handling The API uses conventional HTTP response codes to indicate success or failure. In general: 2xx codes indicate success, 4xx codes indicate an error due to the information provided, and 5xx codes indicate an error with Contazen's servers. ## Expanding Nested Objects Many endpoints support the `expand` parameter to include related objects in the response. This follows the Stripe API pattern. For example: - `expand[]=lines` - Include invoice line items - `expand[]=payments` - Include payment records - `expand[]=client` - Include full client object ## Localization The API supports multiple languages through: - `locale` query parameter (en, ro) - `Accept-Language` header - Default: English contact: name: Contazen Support email: support@contazen.ro url: https://contazen.ro license: name: Proprietary url: https://www.contazen.ro/termeni-si-conditii-de-utilizare/ servers: - url: https://api.contazen.ro/v1 description: Production API server security: - bearerAuth: [] tags: - name: Authentication description: API authentication and test endpoints - name: Clients description: Manage your customers (B2B and B2C) - name: Invoices description: Create and manage invoices, proformas, and receipts - name: Products description: Manage your product and service catalog - name: Expenses description: Track and manage business expenses - name: Expense Categories description: Organize expenses with categories - name: Suppliers description: Manage expense suppliers and vendors - name: Settings description: API settings and configuration - name: Payments description: Payments received against invoices - name: Receipts description: Cash receipts (chitanțe) — standalone or paired with an invoice - name: Company Lookup description: Romanian company lookup (ANAF / VIES) - name: Invoice Series description: Manage invoice numbering series - name: Bank Accounts description: Manage IBAN bank accounts - name: E-Factura description: Romanian e-invoicing status and configuration - name: Supplier Bills description: Supplier invoices imported from the ANAF SPV inbox - name: VAT Rates description: Firm-scoped custom VAT rates on top of the Romanian catalog - name: Currencies description: Currencies enabled for the firm's bill templates - name: Languages description: Languages enabled for the firm's bill templates - name: Conta description: | Public ANAF data for the firm's CUI: fiscal profile (TVA scope, RTVAI, split TVA, status, e-Factura registration, CAEN) and annual balance sheets (cifra de afaceri, profit, capitaluri, datorii, salariați). Powered by the public ANAF webservices (no OAuth required for these endpoints). The data is cached locally and refreshed on demand via the `/sync` actions. paths: /invoices/{id}/payment-estimate: get: tags: - Invoices summary: Predict invoice payment date description: > Returns a predicted payment date for an unpaid invoice using the client's historical average days-to-pay (falls back to firm average, then to `due_at + 7 days`). For already-paid invoices, returns the actual payment date. operationId: getInvoicePaymentEstimate parameters: - name: id in: path required: true schema: type: string description: Invoice ID (czUid). responses: '200': description: Payment estimate content: application/json: schema: type: object properties: success: type: boolean data: type: object properties: status: type: string enum: - unpaid - paid estimated_at: type: string format: date nullable: true due_at: type: string format: date nullable: true days_from_now: type: integer description: >- Days between today and estimated_at (negative if past). days_overdue: type: integer description: >- Days the invoice is already overdue (0 if not overdue). confidence: type: string enum: - low - medium - high - actual basis: type: object description: Data used to compute the estimate. properties: source: type: string enum: - client_history - firm_history - due_date_fallback - actual_payment sample_size: type: integer nullable: true avg_days_to_pay: type: number nullable: true client_on_time_pct: type: number nullable: true meta: $ref: '#/components/schemas/ResponseMeta' '400': $ref: '#/components/responses/BadRequestError' '401': $ref: '#/components/responses/UnauthorizedError' '404': $ref: '#/components/responses/NotFoundError' components: schemas: ResponseMeta: type: object properties: version: type: string default: v1 request_id: type: string format: uuid description: Unique request identifier for debugging response_time: type: string example: 23.45ms ErrorResponse: type: object required: - success - error properties: success: type: boolean default: false error: type: object required: - message - type - code properties: message: type: string description: Human-readable error message type: type: string enum: - api_error - authentication_error - invalid_request_error - rate_limit_error - permission_error - validation_error code: type: string description: Machine-readable error code param: type: string description: The parameter that caused the error doc_url: type: string format: uri description: URL to relevant documentation meta: $ref: '#/components/schemas/ResponseMeta' responses: BadRequestError: description: Invalid or missing request parameters content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' UnauthorizedError: description: API key is missing or invalid content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' NotFoundError: description: The specified resource was not found content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' securitySchemes: bearerAuth: type: http scheme: bearer description: Use your API key (sk_live_xxx or sk_test_xxx) ````