If an error occurs during the sync process, you can go into the sync logs to identify the source of the problem. For example, a format sync error could be an invalid email address.
Go to the Campaigns module, click the ‘Sync Mailing List’ icon and select ‘View Latest Sync Log’.
Select ‘SYNC LOG’ and use the filters to identify the sync error message. In the example, you can see that the source of the error is an invalid email address (empty email).
How to fix Invalid Email Address Format
Go to the Contacts module and select the contact record with the invalid email address. In the contact record, click the ‘Edit’ icon.
Enter the correct email address and click ‘SAVE’.
You can now go back to the Campaigns module and sync the mailing list again.