For the premium features - please make sure that you purchased the packages using the same google account you have configured with your android device.
Then open android settings -> applications -> find zoiper and force stop it.
When you start it again the premium features should be there.
When using SIP protocol one way or missing auido issues mostly appear due to configuration problems. The issues usually appear if the configuration is not adjusted accordingly to the wireless or 3g/4g network.
In most cases this can be resolved by altering the account configuration.
Run Zoiper for Android and go to Config. Select Accounts and click on the affected account. Scroll down to Network Settings.
Try enabling or disabling RPORT for signalling, save the changes and try to make a call.
If the issue persists, open the Network Settings again and activate or deactivate STUN*. Save the changes and make a test call.
• By default, Zoiper for Android is using stun.zoiper.com. Your provider might have their own prefferred STUN server.
If the issue persists, open the Network Settings once again and try enabling or disabling RPORT for media. Save the changes and make a test call.
Try different combinations of these settings to achieve better results.
You might want to try changing the audio driver in Zoiper -> Config -> Audio settings.