I have this exact same question. I tried your steps - however when I went to delete it - It says that it couldn't delete the transaction. Is there any other way to connect an auto generated sales receipt to an invoice?

I created the auto generated sales receipt because I could not figure out in a split second how to have the customer pay the balance on an invoice. Invoice was for $180.00 but she only owed $173.12. She said on her end she could not pay anything other than the $180.00. So I just generated a sales receipt as she wanted to pay right then.