Open Samsung Pay app, press hamburger menu (top left) > Settings cog > under 'Payments' section, press 'Quick Access' - this will likely give you 3 options, to display Samsung Pay option on Lock Screen, Home Screen, or Screen Off. You can, of course, toggle any of these on or off (I have them currently all set to off).
In terms of different function, Settings app > Lock Screen > FaceWidgets.
Depending on your device, you can have quick access on Lock Screen (aka, FaceWidgets) to Music, Today's schedule, Next alarm, Weather, & a toggle for the 'Show always on display' clock.
To access these 'widgets' on Lock Screen, make sure phone display is off, press power button once, and where you see the clock on your Lock Screen (top mid of screen) swipe left or right on the clock. You'll have an infinite scroll list of the clock & whatever FaceWidgets you've enabled in the Settings app.