Hi Paolo,
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.