To re Register your Zoiper Account ensure that all settings are configured Correctly according to the Zoiper set up Solution.
For Android click Here for IOS click Here
If have gone through and everything looks good but your Zoiper is still having issues registering then follow these steps to delete your current account and start fresh.
For IOS:
Step 1: Go to Settings on the bottom right.
Step 2: Select Accounts
Step 3: Select the Account having the issue.
Step 4: On the top right Select the Trash icon. Then select delete account.
You can now Start fresh on your account by clicking Here. If this still doesn't work you may contact support@nwvox.com