The image upload example shown below (w/o space added before MyTestPicture so it would not be auto-linked),

curl -d 'key=<your key>' -F 'media=@ MyTestPicture.jpg' -d 'content=<p>A picture is attached to this post</p>' https://loforo.com/api/post/create

also included in api description page does not work, curl fails with messages shown below and no request is sent.

Warning: You can only select one HTTP request method! You asked for both POST 
Warning: (-d, --data) and multipart formpost (-F, --form).

Use this instead (change -d to -F where needed, remove space before MyTestPicture, don't forget to quote html):

curl -F 'key=<your key>' -F 'media=@ MyTestPicture.jpg' -F 'content="<p>A picture is attached to this post</p>"' https://loforo.com/api/post/create

Using curl version 7.81.0 on Linux with bash shell