Seniors and students
A T4 and/or T4A for the lump sum needs to be entered on to the return. The T1198 is just a request to take the income from the T4 and/or T4A and use a special tax calculation to tax the retroactive amounts in the way they would have been taxed if you had gotten them in the right year.
Was the T4A that you entered for the lump sum payment, if so, please double check that you've entered the amounts in the correct boxes. If you didn't get a slip for the lump sum, check on CRA's MyAccount to see if there's something there, or contact whoever is issuing the payment to get a copy.
