Hi there Accounting4050-2020,
Thanks for reaching out about invoice creation. Quickbooks Desktop is a great tool able to help you create invoices so you can inform your customers of the services they've purchased. I can point you in the right direction for assistance with that error.
For assistance with the error if each line is completely filled out correctly, I recommend reaching out to the QuickBooks Desktop outside of the Community. They'll be able to view the transaction with you in a secure setting to assist in getting it completed. You can reach them using the methods outlined in the QuickBooks Desktop software support policies.
If you have any other questions, feel free to reach out here.