Samsung Pay does not need to be specifically coded in by the manufacturer of a point-of-sale terminal or accepted by a store in order to work, due to its use of magnetic secure transmission. Any user whose bank is compatible with the service can pay anywhere that they would normally use their debit card, via either their phone or certain Samsung smartwatches. Those smartwatches, however, require a Samsung phone in order to use Samsung Pay. Everybody has their taste in Android devices, which is the beauty of Android; not everybody is willing to get a Samsung device just to use Samsung Pay. With adoption of Android Pay and Apple Pay still somewhat low, it could even be argued that the only thing keeping Samsung Pay from mass adoption is the fact that it's tethered to Samsung phones. The Gear S3 was apparently supposed to help with this, and the latest update reportedly activates this function.
In response to a tech site's article about the Gear S3 posted on Twitter, user @internetusr mentioned that they returned their Gear S3 because they could not use Samsung Pay with their non-Samsung device. The official Twitter account for the Samsung Pay service saw the Tweet and replied, saying that the feature is available as of November 23rd. They went on to say that those who wanted the functionality simply had to update the Gear Manager app on the phone that the watch was paired to.
The Gear Manager app is available on Google's Play Store and will run properly on any phone sporting Android 4.4 (KitKat) or higher. This means that just about anybody can now use Samsung Pay without having to sacrifice their love of stock Android or Sony's boxy designs, for example. It should be noted that this function has yet to be tested on phones without Google Play, such as some Chinese devices or those running custom ROMs without Google's app suite, and also has yet to be tested on rooted devices. Since payment apps, most notably Android Pay, typically aren't very root-friendly, those who aren't willing to give up features like navigation bar customization and CPU frequency control should probably not get their hopes up.