Thank you both for the ideas.. I have been looking into the practicality of all of them.
Unfortunately, I still cannot work out a very practical solution. Let me explain the game slightly further. A player can give "lives" (tokens) to another player, but I would like this to be done without needing internet access. The process would be something similar to:
Player one selects how many lives to give player two.
The two devices start to communicate.
The lives are removed from device one and added to device two.
A confirmation needs to be received by each device before the new totals are tallied.
NFC originally looked to be best to achieve this, but I have read that NFC is being deprecated by Google, and in fact the cup game did not work on my phones. (A Samsung S7 and S10)
Using QR/barcodes was an option, but for the "transaction" to totally complete, there would need to be a lot of scans from both devices - not very practical.
Bluetooth is a possibility - but from what I can gather, a search of all discoverable devices needs to be done first and then both devices paired. Lots of time required up front with lots of user interaction. Unless it is possible to (eg) scan a barcode and know what device to connect to?
I wanted something almost as quick and easy as (eg) paying for an item in a shop with your phone.
If you have any suggestions, they would be massively appreciated!