I have Zoiper 2.6.31 with Android 8.1.0 on a Samsung J7 (2017).
When I enter a phone number to the contacts in the international context like
the contact has "automated" generated spaces in the phone number like
+49 5131 1234 98765
I can't delete this spaces in the Android contact list and these phone numbers work fine with the normal phone
...... but not with Zoiper! No connection will be astablished.
When I dial this number manually (without spaces) it works fine!
I could not be the only one with this problem!