[API] Uploading file via API to existing record by ID

[API] Uploading file via API to existing record by ID

Hello,
I'm trying to uploasd a PDF to an existing record using its ID via API as written in the instructions (https://www.zoho.com/creator/help/api/v2/upload-file.html ).

I succefuly created records on the form in my app.
Then I took the record ID from the report and wrote it into the request URL for file upload. 
The result of the POST command was : {"code":2930,"message":"Error Occurred. We are sorry for the inconvenience."}

I am certain that I followed the documentation to the letter, please advise.

Thank you very much!
Yossi