Hang on… This thread has gotten confusion about what and who is checking.
Stop, breathe…
For a Bonjour (Direct) Connection between machines…
Machine A has the database to be Synced.
Machine B wants to Sync with Machine A.
Bonjour:
Machine A has it On.
Machine B checks the checkbox to connect to Machine A.
Machine B sees the list of available databases on Machine A.
—> If the database is only on Machine A, databases will be listed in the Remote section and will need to be imported. Right-click the desired remote database and choose “Import Database”. You will be prompted to Save the database on Machine B. It is now Synced and a client of that database on Machine A.
—> If the database is on both machines, they will be listed in the Local section. Machine B would check the checkbox and it would Sync with Machine A. It is now Synced and a client of that database on Machine A.
As the Bonjour connection is bidirectional by design, changes made on Machine B will be pushed to Machine A as expected.
Note: In the case where you already have a copy on both machines, technically either machine could act as the host for the Sync, but you should pick one host only. In this case we chose Machine A.
Note 2: There is nothing new going on here. It is the same thing as connecting to a cloud account. For example, when you connect to your iCloud account, you are a client of the host (server). If you make a change to your iCloud Drive folder on your machine, the changes are pushed to your iCloud account. Changes to iCloud from another machine are pushed to your machine. The iCloud server never becomes a client of your machine. This is the same thing and setup as our Bonjour Connections.