Unfortunately, this is a program bug that they won't fix. The special calculation goes back and forth to get a final number. The 'bug' happens when the back and forth calculation goes past the $47,520 amount. Rather than continuing to calculate it until it gets an answer, it stops and says you don't qualify.
So in direct answer to your question about how to get the correct amount, you either need to manually do the calculations (which is gruesome), use another software, or go to a tax professional.
Sorry for the bad news. I wish they would fix it (I pointed out the problem in 2015, but they have ignored most of the things I have pointed out).
