So I followed your suggestions and in the end I replaced all with your zip file.
Same thing, it does not show error message when I click submit and have not filled out all the fields.
What could it be? the hosting server?
Btw I tested the other one I initially said worked. but it does not, it has the same flaw, I don't know if it did before since I wasn't testing on this specific problem, I might have filled out all the fields every time while testing...