Several things happening here. You should start with our forms debugging playbook, here: [Support Guide] Form problems, form debugging, 404 when submitting . It speaks to your 404 page issue, and also to why we aren’t receiving your submissions, which I will recap in brief here, but you really need to read that whole post since it is all directly relevant to your situation:
that is not the right content-type as you’ll see in the debugging guide
if you don’t have any fields defined in the HTML version of your form (I don’t see them, but maybe you just cut it off?) we won’t save any fields.