We have finished integrating Apple Pay in our app and our payment processor is requiring us to send the 3dSecure version used for apple pay (2.1,2.2,2.3,etc.). I believe this only applies to mastercard but would appreciate if anyone has run into something similar and what you specified. I have not been able to find anything in Apple's documentation specifying the version that is used.
Apple Pay 3dSecure Version for Mastercard
Apple Pay doesn't seem to provide the 3DS protocol information directly.
But as far as I know, this information should be returned in onlinePaymentCryptogram - but depending on the card brand, how you extract that information will differ.
I would recommend talking to your payment processor, they should have the information on how to extract that information from the cryptogram.
Or maybe you can ask if it's acceptable to send 2.x instead of the specific protocol version.