Well, it keeps saying (at/on the Watch) that Google Messages needs to be installed and set as default. There isn't anyway that I am aware of for how to set that other than setting it at/on the Phone.
Am I missing something?
IDK. Like I said, I have not had this issue so I'm not much help. I'm pretty sure I did not do anything special to set up google messages as a default. Have you tried to uninstall then reinstall Messages? Maybe there was something in the install procedure that made it work. Or can Samsung messages be uninstalled on the watch and phone?