I received back pay in the 2023 tax year. My pay increased but I did not receive the payment until 2023. How do I report the lump sum payment on my 2023 tax return?

Are you using TurboTax CD/Download or TurboTax Online? Did you receive a slip for this lump sum?

I'm using the online version. And no slip but it has it accounted for in box 40 on my T4.

If it's already on your t-slip then there's no need to enter it anywhere else.