Id of invoice

Filename should be with proper extension i.e. fileName.extension

File content should be base64 encoded content of the file you are trying to upload.

if you are providing the file URL, you do not need to provide the content

The content-type of the document you are sending. When using a URL, this generally isn’t needed, as the responding server will deliver a content type. This should be included for encoded content.Click here to see examples - https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types/Common_types