The income Find search function returns an error using any search terms, including the literal string "T4". There doesn't appear to be any other way to submit T4 data.

I’m sorry you are having this problem. This is a known issue with TurboTax Online Free that seems to affect Chrome users. We are working to fix the issue, but in the meantime, there is a workaround.

Close the error message and the “Find” tool pop-up. Then click the button “Continue Without Income”. The “Find” tool should now function normally, and you can now use it to add any T-Slips you need.