I’m calling the primary switch the one connected to the load. Associate the secondary to the primary with group two. Do not modify association behavior on either device. This will allow you to turn the load on/off from either switch. With just the association setup the secondary switch did not indicate the proper state and their states in ST app were not correct. I then setup rules to mimick states using smart lighting. Ie if primary turns on/off then turn on/off secondary and vice versa.
This will probably work for other hubs but I’ve tagged it smartthings for now.