There is a BUG with this mission. You'll get some text from it, but you have to change it to get it to work for the answer.
I'm not sure if I can say this part or not, so please just remove it MOD if it is too much information.
When you get to the end where you THINK you have the answer, you have to remove the last 2 characters for it to accept the answer. Whoever developed this left those off for some reason. If it weren't for that, this challenge would be quite easy. I had it solved over and over again for a long time without that hint and was struggling. I got the hint that the accepted answer was slightly different than the answer I had, so I needed to alter it. After removing the last 2 characters, it worked.