There is actually a BUG in the documentation
curl -k -XPOST https://127.0.0.1:5000/api/records/jnmmp-51n47/draft/files -H "Content-Type: application/json" -d '[
{"key": "leaf_doge.jpg"},
]
'
Should be
curl -k -XPOST https://127.0.0.1:5000/api/records/jnmmp-51n47/draft/files -H "Content-Type: application/json" -d '[
{"key": "leaf_doge.jpg"}
]
'
I was able to complete the file upload after this was fixed