Haha I was using the API incorrectly. I was pushing the image in form.custom_thumbnail while form.url was empty. Apparently, u can’t do that.

If u have an image only post, then u have to put the image uri in form.url. the custom_thumbnail is only there if you already have some other link.

Lemmy’s documentation is really lacking. Unfortunately, contributing to it is a little complicated too (for lemmy-js-client), that is