Form Base always successful!

I’m new to this community so hello everybody,

After reading about Form Base here I can’t find the answer to my problem.
So here it is: I’ve used Form Base, entered all the fields with relevant emails (and yes the From address matches the domain of the website) and absolutely nothing happens.

I would have checked my web host to ask about php version but then I realised that if I submit the form I always get a Success Alert message even when I don’t fill in anything, or if I fill in the form with complete rubbish (not even an email address).

What am I doing wrong?