A receipt is not a thank you.
It doesn't show gratitude, appreciation or awareness that something good has happened.
It just shows that something has happened. It may be good (for the customer to know you know they did or expect something - but that's about it).
If you acknowledge transactions, orders or gifts to your business or organization with a receipt - that acknowledgement is a receipt... not a thank you.
It's the least you can do.
And you can do better.