Unclear from documentation how to supply extra fields to upload POST requests.

[mstone121]

From the documentation:

Send it all the data that your Collection requires

payload/docs/upload/overview.mdx

Lines 306 to 308 in 4c3e41b

	To upload a file, use your collection's [`create`](/docs/rest-api/overview#collections) endpoint. Send it all the data that your Collection requires, as well as a `file` key containing the file that you'd like to upload.
	Send your request as a `multipart/form-data` request, using [`FormData`](https://developer.mozilla.org/en-US/docs/Web/API/FormData) if possible.

This makes it seem like I can just add extra fields to the form data, but this didn't work. I had to add a JSON string of my data to the _payload field:

body.append('_payload', JSON.stringify({ ...extraFields }))

I think this could be more clear from the documentation.