From your T4A(P) slip you need to add the same information shown in the boxes on paper slip to TurboTax. Be sure to include the number of months shown in Box 21 or 23.

To add any of your T-Slips in TurboTax Online, go to Income > T-Slips > select the slip you want to enter (in your case this would be T4A(P) - Canada Pension Plan Benefits). Then when you land on the "summary" page for that slip, select "Enter New T4A(P) for "yourname). Make your entries on this screen from the corresponding box numbers shown on your actual slip.

I am doing my wife's and my income tax,  I enter  T4 (OAS) on each of our slips and the same for both T4 (P) slips.    I am the only one receiving T4  for employment which I slit with her on the return.    The total on the summary sheet show my income for 3 slips correctly, however, of the !4,072.64 I split with her (7036.00) is still showing on my line of summary sheet and $3520.10 added to her income on summary sheet, which  increases our total family income to $46,466.26 from actual income for both  of $42946.16.

All of the slips are entered with actual amounts shown, the difference in the summary sheet seems to be about half of the income I entered which was slip with my wife which was total amount of 7036.10, (3518.00)

I split pension from my T4A, ( $14072.64)  which was 7016.00,  her total income than became 12211.25  from original amount of 8691.17 however my income  stayed the same, which increase total  income by approx. $3500.00.