My client says they never got the invoice
Check the audit trail on the invoice. It records when it was sent and when the client first opened the pay link.
Open the invoice and look at the audit trail on the right. It shows the moment the invoice was sent, and if the client has opened the pay link, the moment they did. That usually settles the question on its own.
If it was sent but never opened, it is almost always spam filtering. Invoices sent from a free email address are filtered more often than ones from your own domain. Ask them to check their junk folder, then press Send again.
Faster still: copy the pay link from the invoice screen and send it to them directly on WhatsApp. The link works on its own, without the email.
If not, the assistant in the corner can dig further, or a person will pick it up by email — Mon to Fri, 08:00 to 17:00 SAST.