Hi there, @efalconer!
It'll be my pleasure to assist you in printing a check with an invoice number attached on it.
You'll have to make sure that the invoice number was typed in the memo field on the lower part of the checks.
Please see screenshot below for your visual reference.

You can also read this article about printing checks: How to Print Checks?
Feel free to leave a comment below if you need any other help. Have a great day!