[Samsung Galaxy Watch 4] gyrga:
(updated Sept 5 to include some VPN steps that were missing)

After a lot of attempts with a varying degree of success, I think I've finally managed to make it work in an unsupported country (I am in the Netherlands, but I think this method will work for any region). The Google Pay has been on my watch for more than 24 hrs without disappearing, and I also was able to pay with the watch!

Here are the steps to get it working:

Not sure if this is actually needed, but I’ve reset my watch to UK region instead of NL first. I think this is not necessary, but I am not resetting my watch again to try it 😊

Sideload this version of Google Pay to your watch: https://www.apkmirror.com/apk/googl...wear-os-2-135-389276953-android-apk-download/. You’ll need to enable developer mode on your watch (Settings => About watch => Software => tap multiple times on "Software version") and “adb debugging” + “Debug over wifi” in the developer options. Then sideload the gpay app through adb or an app like Bugjaeger. DO NOT OPEN THE APP ON THE WATCH YET!!!

Turn wifi and gps off on the watch. Turn off the watch.

VPN on your phone to a country where Google Pay is supported on the watch (I used UK).

Turn on the watch and then start Google Pay on the watch while wifi and location are off, and VPN is active on the phone. It should finish installing properly and appear in the NFC menu (might need another reboot if it does not). You can then disable the VPN on your phone.

Add your card to Google Pay on the watch. Any card will work so long as a) it has a regular 16-digit number (so IBAN cards, unfortunately, won’t work) and b) comes from a country where Google Pay is supported on phones (for example, in the Netherlands Google Pay is not officially available on wearables, but since the phone version works fine, you can still add a Dutch card on the watch with this method).

Now, the most important part: after some time (in my experiments it was anywhere between 5 minutes and 5 hours), the Google Pay app will get disabled and disappear from the watch. You might be able to re-enable it from your phone’s Galaxy Wearables app (list of apps => app info => Google Pay), but it soon gets disabled again for good and it’s not possible to re-enable it again through the app, so you’ll have to uninstall it from the watch and then sideload it again. The solution is to pay with the watch in a store before Google Pay gets disabled: it seems that after the first payment some Google Pay and/or system settings are updated, so the app won’t get disabled anymore!

Important: if you have a non-regular card added to your phone’s Google Pay (for example, IBAN card in the Netherlands), then Google Pay on the watch will give you an error "Something went wrong, please try again" after trying to get your cards during step #2. You can try to remove this card from Google Pay on your phone, which would allow you to proceed with steps #2 and #3 on the watch. However, after this on my phone I got an error “Couldn’t finish setup to pay in stores. This phone can’t be used to pay in stores. This may be because it is rooted or altered in some other way”. I am not sure what exactly is broken here, but a solution for Samsung phones is:

Flash a different region firmware with Odin using HOME_CSC to keep all the info intact. I think it does not matter which region you choose as long as it supports Google Pay. I’ve randomly chosen a Vietnam one.

This seems to fix Google Pay on the phone and now you should be able to add your card back without any errors. Perhaps there is an easier way to fix Google Pay without reflashing, but nothing else worked for me.

Flash your original region firmware with Odin (and again use HOME_CSC or you’ll lose your data!). Now you should have fully working Google Pay both on the watch and the phone. Your IBAN card will be working only on the phone, though.