Upload an attachment to a Purchase Order

Required permission: Purchase Orders - Edit

Accepts a single file via multipart/form-data. The file's actual content (detected via magic-byte sniffing) must be one of the allowed types (JPEG, PNG, GIF, PDF, CSV, XLS, XLSX) and the filename extension must match the detected type. The declared Content-Type header is informational only and is not trusted. Maximum file size is 10 MB. A PO may have at most 10 attachments.