Create Case - No selected contact: Contact ID
If you are receiving this error, it is most likely because you're trying to create a Case object and you do not have an email field mapped.
Case objects have an invisible trigger on the Salesforce side that fires based on the email field of the Contact object. If the Case object isn't associated with a contact, then that trigger fails with this error.
1. Associate a contact with the case.
2. Turn off the "Trigger other emails" at the bottom of the connector: