After the synchronization with the Zivver Synctool, you get this error.

Error processing <full_name> (<primary_email>) with status code BadRequest: Error creating alias: Alias is a guest: <alias_email>

Cause

The already received one Zivver message or more as a guest recipient. The Synctool cannot combine the guest account with the primary Zivver account.

Solution

Enable the setting Merge guest account into primary account if guest account is an email alias under Syncing > Synchronization Options > Special functions (only manual sync) and run a Manual Synchronization.