This endpoint allows you to attach a single file to an existing invoice record. Unlike the Upload Invoices (with AI) endpoint, this endpoint does not create new invoice records and does not perform any automatic data extraction.

When to Use This Endpoint

Use this endpoint when you want to:

Attach a file to an invoice record that already exists in the system
Add supplementary documents (supporting documentation, receipts, etc.) to an existing invoice
Upload a file without triggering AI-powered data extraction

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Important: This endpoint does not trigger the content extraction process. The file is simply attached to the invoice record without any automatic data extraction or purchase order linking.

Key Features

Requires existing invoice: The invoice record must already exist before you can attach files to it
No data extraction: Files are attached as-is without any AI processing
File type specification: You can specify whether the file is the primary invoice document (INVOICE) or a supplementary file (OTHER)
No purchase order linking: Purchase orders are not automatically linked when using this endpoint

The request must use the multipart/form-data content-type.

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Recommendation: If you need to import a new invoice with automatic data extraction, use the Upload Invoices (with AI) endpoint instead.