Get a KYB document upload URL

Two-step upload, step one. Returns a file_id, a presigned url, and the headers required to PUT the file directly to S3. The URL is valid for 5 minutes and accepts a single PUT.

Step two: call POST /api/external/customer/{customer}/document with the same file_id to register the document.

Max file size 25 MB. Allowed types: application/pdf, image/jpeg, image/png. Files outside these limits are rejected at registration time.

The customer must be of type business. Individual customers do not use this endpoint — they use the legacy file flow (POST /api/external/file/get-presigned-url followed by POST /api/external/customer/{id}/files).

Required scope: customer:write.