Sync Contacts from Gmail to Salesforce via Einstein Activity Capture

This is working as designed. Upon completion of the set up of the EAC, it creates the label 'Salesforce Sync' automatically. For the Contact to be synced successfully by EAC, it needs to be associated with the label. Below are the steps on how to set the label for Contacts within Gmail:

1. Click on a Contact in Gmail/Google Contacts
2. Click on the pencil icon to manage labels
3. Select the Salesforce Sync label to flag the Contact for sync.

Note:

1. Allow EAC to detect the new settings for the Contact. Check the sync's progress after a few minutes or so. You may also search for the email address in Salesforce to see if it is already available. 
2. Salesforce Starter Edition doesn't need Contacts to be labeled as Salesforce Sync as with this edition all Contacts from the uers's root Google Contacts folder are synced.
3. See Also
   How Contacts Sync with Einstein Activity Capture