What content types are allowed in the multipart format using API?

The content types allowed are the standard ones, some examples are:

Application types

• application/pdf: A PDF file
• application/zip: A Zip file
• vnd.openxmlformats-officedocument.wordprocessingml.document: A MS Word document

Image types

• image/apng: Animated Portable Network Graphics (APNG)
• image/avif : AV1 Image File Format (AVIF)
• image/gif: Graphics Interchange Format (GIF)
• image/jpeg: Joint Photographic Expert Group image (JPEG)
• image/png: Portable Network Graphics (PNG)
• image/svg+xml: Scalable Vector Graphics (SVG)
• image/webp: Web Picture format (WEBP)

More detail:

• https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types 
• https://www.iana.org/assignments/media-types/media-types.xhtml#application