Question about purchasing Glyphsmini from the App store

I just bought Glyphsmini from the App Store, and I haven’t got a receipt yet. Do you know if it takes a few days to get it? Just worried, because in the future I might want to upgrade to Glyphs and I know I will need the receipt.

Where can I find my serial number if there is one.

There is not serial number.
You should get a receipt, the same you get if you buy something from for the iPhone or from iTunes. If it not arrives in a couple of days, check you spam folder and then ask Apple.