What is DTMF?
DTMF tones are sent when browsing voice menus. Ask your VoIP provider which DTMF type to use with your account.
Changing the DTMF type in Zoiper 3
First you will need to know what type of DTMF is supported by your VoIP provider.
Open Settings -> Preferences -> Accounts -> Select your account and select the Advanced sub-tab
Use the drop-down menu to change the DTMF type according to your provider's recommendation.