DTMF and keypad ( on Ios )

If the keypad does not work, then you might need to change the DTMF type according to your VoIP provider's recommendation.

Start Zoiper for iOS and go to Settings -> Your registered account (You should see Account name) -> Features

Select any of the supported DTMF settings: Inband DTMF | RFC 2833 | SIP Info | Disabled