[dingwallr]

Assuming we're talking about bank card transactions, SMS confirmations for every purchase are not really possible. The issuing bank has a very short amount of time to respond to an authorization request message. By the time you've sent an SMS, unlocked your phone and replied, the merchant terminal or payment network operator would have timed out.

All the rest are great ideas though! ;)

[peteretep]

Decline the first one, send an SMS, user interaction, run the transaction again, now it goes through. This is pretty much exactly how I use my Revolut card at the moment.

[ardaozkal]

Denials can (and do) cause issues at times. At least weird looks.