Hi,
just to mark this thread as "definitively closed": the mistake was mine and the previous suggestion is irrelevant.
My APP wasn't receiving SMS because... I wasn't sending SMS to it.
Instead, I was sending "chat" messages.
Chat service is enabled by default on new Samsung devices, 'SMS mode' must be activated manually.
Unfortunately the messages appearance is the same of SMSes, and they are generated by the usual SMS APP.
My apologies.
Best Regards,
Claudio