Since Android 5.0 the new notifications have been introduced. Moreover, the standard dialer call notification is 'overhead', i.e. non-blocking. This type of notification is supported in Android Wear without any tweaking - user can (a) see who's calling, (b) answer/reject the call.
But Zoiper keeps using 'old' (blocking) type of call notification - which is not displayed on Android Wear devices, and thus incoming calls via Zoiper are lost/missed (most Wear users prefer to disable all sounds on the phone while a Wear device is connected).
One way to fix this is to support the new system.
Another fix could be support for Android 'intents', accessible e.g. from Tasker. If we could intercept an 'incoming call' intent (and possibly respond with an 'answer' or 'reject' intent) that would at least be a reasonable solution.
Currently Zoiper is unusable for users of Android Wear who choose to mute all notifications on their phone.