I created a form and when I submit, it goes through but there is no "success" or "failure" message on Apex. I tried debugging it and got this message:
"Page contains page items/buttons which are not assigned to a region!"
I looked at the page definition and it seems like everything is assigned to a region. Much appreciate your help.
For your message, the relevant branch needs "include process success message" to be checked - and a value in success/failure in your process.
Check the submitting & landing page for items not in a region. Under the items section there may be items listed separate to those under specific regions.
It's possible these are related, but not guaranteed.