Are you using TurboTax CD/Download in Forms mode? If so, you should be able to directly enter amounts in those lines.
For more assistance with this issue, please contact us by phone. To talk to our phone support team, visit https://support.turbotax.intuit.ca/contact/ . After entering some basic info about what you need help with, the page will give you the phone number for the team best suited to help.
I had to call your tech support to solve the problem. Very simple solution - I increased the Font and I could then enter amounts to both lines. Suggest TurboTax have an error message in future giving solution instead of your irritating "bing" every time I tried to enter amount! I expect more from TurboTax!
You may enter the total amount of support payments received for line 12799 and the taxable amount for line 12800 with the EasyStep.
Click the find button and enter Support and select Support payments Received
Proceed to the next window to enter your amounts as demonstrated below:
When going to the T1 General form, you need to select the correct return for the amount to appear on the lines 12799 and 12800. As shown below:
I hope this information is useful!