I have exactly the same issue with Sipgate and iPhone 6, I paid £6.99 in app purchase for the G729 codec but it does not activate anything. I have tried to contact Zoiper but as I am using the free app version there is no support. So if anybody on this forum can help that would be awesome...
Any body know how I set this up to receive calls over 3G/4G ?? Or what I have to do to activate the in app purchase.....I have tried the restore purchase button etc etc..
Thanks,