My customer says they did not receive the invoice email.

Check the billing email on the customer record first — that is the only address the invoice goes to — then ask them to look in spam. The email log tells you whether Gridbind sent it at all, which separates a wrong address from a filtered message. You can also share the invoice as a link instead: the share page shows the document and, where online payment is set up, lets them pay from it without an account.

The email log records the recipients, the subject and whether the send succeeded or failed. It does not track what happened after the message left Gridbind, so a message accepted and then bounced still shows as sent — but between the address on the record and the log entry you can usually tell which of the two it is.