Mobile phone verification failed

The FAQ opens, but the Inquiry section does not, so I am submitting my inquiry here.

I use two mobile phones, so I signed up for both and verified my main phone. However, when I tried to verify the third one, it wouldn't work, saying I am already a verified user.

I confirmed that other similar apps work, so it is true that I am upset that only Unpa does not. Even so, if there is a rule prohibiting one person from using two phones, I will cancel my subscription.