To use the Samsung Pay on a Gear S3 with a Huawei you need to install the Samsung Wear app and pair with the watch.
When you open the app, you will find a "Payment" option where you can open Sansung Pay. It is very slow, so just tap once and wait till Samsung Pay opens.
It will ask to install some Plugins. Just do it and it will work. (Well, it worked for me with a S3 on my P30 Pro).
As a solution I suggest a duplicate of the SIM card that has not been used with an NFC Samsung payment after.
A duplicate card does not cost expensive, about € 5 and can solve the problem, since there is a link between Service, SIM and the NFC in a Samsung Mobile, I guess for the MST chip.
Please comment on the answer and select as a solution if it worked for you, so that other users of the Community can be aware of it.
Greetings to all