I paid for gas at Shell with Apple Cash and it took $100, but it only cost $50. Where is my $50. balance?

Apple Cash is more like a debit card than a credit card.

Most gas stations will 'reserve' a set amount when you start pumping, to ensure there are funds available.

Once you finishing pumping and finalize the transaction, the gas station takes the money owed from the reserve and releases the remaining balance.

The release can take some time to show up on your account.

This is true of all debit cards, not just Apple Cash - and most gas stations have a sign at the pump regarding debit card transactions, since most people don't realize this is how it works.

At the moment there's nothing you can do beyond wait for the transaction to post and the reserve to be released. I guarantee you that going back to the gas station to complain will just waste your time.

Sometimes a gas station will charge you more than what you paid for if you use a credit card.

The $100 should fall off in a few days and you will be charged for $50.

When I use Apple to pay for gas, I prepay at the register. I'll estimate $40 and if the tank only took $20, then I go back and ask for the remaining $20. They hand the remaining balance in cash.

If you use this method, then you may have not picked up your remaining balance. Check with the gas station.