Take this for what it is, advice from an internet rando.
A popular sport is on the back of the hand, just above the wrist
but there are other options.
check out
Personally, I would suggest P1-P4 They are all great positions for presenting to a reader.
If I had to pick one, I would steer more toward P4…or P3 just because of the wrist flexibility and ergonomics to interact with a reader.
Thats why I put my custom payment in P4.
Keep us updated
Good luck