As per the Canada Revenue Agency(CRA) Netfile Restrictions. Error code 31 is: The identification information given by Service Canada when your social insurance number was created does not match the information provided to the Canada Revenue Agency.
In your case the information does not match as there is no information entered yet because you never filed your income taxes.
Most first time filers have to mail in their returns. After you get your Notice of Assessment, you will be able to sign up for your MyAccount with the Canada Revenue Agency (CRA), and Netfile next year.
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