Unfortunately, you will need to print to mail your 2018 tax return. 

Go to File on the left hand side on the bottom- you will then choose Print to Mail instead of NetFile. You will notice that you will only have a few pages with a barcode, that is a condensed version of your income tax return and it is all that CRA needs. 

Where do I mail my federal tax return?

Thank you for choosing TurboTax.

Thanks so much for your response. I mailed it in. 

have a great day!!!

jennie

Or, simply remove the OVERPAYMENT amount from Box 16 on the T4, then successfully EFILE it.  Government will just eat it up anyway & the Client will never see it.