What is the result? It works now? How did you managed to do that?
Had the same issue. Incredibly frustrating. The only fix was for me to install the APK manually. I found it here: https://www.apkmirror.com/apk/samsung-electronics-co-ltd/samsung-pay-watch-plug-in/samsung-pay-for-g...
Ok, just to clarify, did you download it with your phone, or with your watch? I downloaded it with my phone, and got prompted that it wasn't from a trusted source-which I approved so that I can download it, but after openning it, it says that my watch may not be supported.
Thanks for your reply