We'll get this sorted ASAP! The good news is that, even if they don't have a copy of the purchase confirmation/receipt email, the nonprofit will have the purchase on record.
Anyway, the first place to look would be in your email inbox. All receipts are automatically sent there. (You can search "BetterWorld" or "[email protected]").
The second place you can find receipts is in the My Account area.
Step 1: Head to My Account, and click on the product that you're looking for a receipt for (i.e. a donation receipt, a ticketing receipt, and so on).
Step 2: Click "View" next to the transaction to see the receipt.