When you type the SIN number, make sure you don't add spaces or any invalid characters: https://turbotax.community.intuit.ca/community/errors-confirmation-messages/help/error-message-inval...
If you are filing a couple's returns, each person should have their information page with the SIN number entered as explained above.
If you are filing someone's else return separately, make sure you don't continue with your profile instead start a new return from the main page.
I hope this was helpful
