Where do I enter Box 20 from my T4A(P)?

Box 20 includes any benefits shown in boxes 14 to 19. These boxes show what kind of benefit you got. TurboTax calculates box 20 from these amounts, as it is only a total. You can’t enter it directly.

Please contact Service Canada to get a corrected slip: https://www.canada.ca/en/employment-social-development/corporate/contact/cpp.html