I just started having the same problem with my FiOS Mobile App on both my phone and my wife's . . . both androids. I think it started on June 10th.
I've checked to confirm that login and password were correct and made sure there were no special characters in the password, but still not working.
Spoke with customer support yesterday. They advised that i should reset my password which I tried several times while on the phone with support and still not working. Support representative hung up on me instead of continuing to try to address the problem.
Sent report of problem to Verizon and received an e-mail advsing that i should check to confirm i had my password correct.
Thanks Verizon . . . appreciate the help.