Every email Money sends for you comes back to you as a receipt. Per diem requests, cash requests to the business manager, settlement emails, reports and summaries: once it goes out, ATOM emails you "Sent: [subject]" with who it went to, the time it went (Central time), and a copy of exactly what was sent. The green message on screen also says "A receipt is in your inbox."
The receipt proves ATOM sent it. It can't prove the other person received or opened it; if they say they never got it, check their spam folder, then send again.
No receipt comes when you were already on the To line (you have the email itself). Signing receipts that crew get after they sign for per diem are separate; those go to the person who signed.
Merch settlements too. When a signed merch settlement is emailed from the booth, each person gets their own copy (venue rep, seller, you). You then get one receipt listing the others it went to (the venue rep and seller), with the time and a copy. If it only went to you, there is no receipt, because you already have the email.