Fix malformed multipart body

[shemogumbe]

Opened to replace #1069 which seems to be from a fork I can't access

Fixes #1068

[andrueastman]

Looks good from my end.
I believe you'll need to add at least one conventional commit to trigger release and update the changelog with release please.

[baywet]

Thank you for making the changes!

@shemogumbe please make sure you squash merge (not merge) with a conventional commit to trigger the release.