I just experienced the same issue.  We had an employee pass away, and we paid a death benefit to his wife.  This needs to be reported on the T4A, box 106.

QB automatically calculates, and populates box 48.  As with the OP, I tried to overwrite it, and even spent 1h on the phone with support.  They were beyond clueless, and ended up telling me that "Pro" doesn't have this feature, but "Premier" does.

Intuit, why do you have such contempt for your users?  You continually increase our subscription fees, but are completely deaf to the feedback on this form.  It is two years after the original post, please don't tell me to submit feedback given that it has already fallen on deaf ears!