Uploads a media file and returns a URL you can use in messages.

Before you call

• Send the file as multipart/form-data in the file field.
• The file type must be one that WhatsApp supports, and the file must be within WhatsApp's size limit for that type.

How it works

• Returns mediaUrl and expiresIn (in seconds).
• The URL expires and the file is deleted after 1 day, so send your message before then.
• Returns 400 if the file type is not supported or the file is too large.