Had a number of occasions when I have send invoices and they haven’t been received. Other that the app saying sent, it would nice if I could see a copy in a sent items??

Hello Big_air_162, 

Welcome to the Community page, 

Have your customers checked that the invoice you have sent has not inadvertently gone into their spam or junk rather than their inbox?

Is this happening more when you send the invoices through the app or when you're in the web browser? 

Are you able to send what happens by sending your self a test invoice and seeing what happens?