Paying by card is not one event. It is two, and hardly anyone knows there are two.
The first is authorization. In about a second, the shop asks the bank that issued your card a question: does this person have it, and do you approve? The bank looks at the line in its ledger, answers yes or no, and holds that amount aside. That is the little word pending in your app — the grey line that has not quite gone through.
The second is clearing and settlement. Hours later, sometimes days later, the money actually moves between the banks.
Which means that at the moment you paid, not a penny moved. A permission moved. You did not copy anything and you did not send anything — you asked somebody to change two lines, and they checked before agreeing. That check, repeated billions of times a day, is what stands between digital money and being spent twice.