New collection <name> is available for subscription. Publisher: synchronization partner <(null)>. (4222396)

You have just installed a new Branch and you see the following event and no new publications are available to subscribe to for that partner:

New collection <name> is available for subscription. Publisher: synchronization partner <(null)>.

1. Unregister the Sync partner referenced in the event from the HQ, and remove the HQ from the branch as well.

2. On the HQ Side: Generate an existing Key, and send it to the Branch and apply it. 

3. On the Branch side: Generate a new key with a new password and send it the HQ and have the HQ apply it.

4. Test mail routing between both sites by sending emails back and forth through OWA with the service mailboxes.

Note: When testing mail flow if the Synchronization Service is running you may see an event saying "Invalid Messages received from <…>"