Can't hear anything after dialing # from iPhone 6Plus

Question

I can place outgoing calls ... and it rings on the other end (I have tested with two office phones).  But I can't hear anything.  I'm used the paid version of Zoiper (Business?) that I bought from the Apple Store.  

Answer 1

This could be a network related issue.
If using a SIP account, disabling or enabling STUN could help.

• - rport and stun
Please try to enable or disable "STUN" and Rport for your account.
"STUN" ands Rport are located in "Settings"->"Accounts"->your account->"Network Settings".

Please try allowing the microphone usage in the iOS settings:
IOs Settings -> Privacy -> Microphone -> then enable Zoiper.