Can't access opt-out list - FORBIDDEN - Resource not found or you don't have the permissions to access this resource
This means that the user doesn't have access to the contact list. Normally this is because the contact list was created by another user.
To give another contact permission to send to all contact lists:
- Log into the account dashboard
- Click on 'Accounts'
- Click on 'Add/Edit Subaccounts'
- Click on 'Edit' next to the user
- Check 'Share Contacts'
- Click 'Save'
If the 'Share Contacts' permission is enabled, that user can access all other contact lists under the main account.