The capx you shared somehow got corrupted - there is no Files subfolder in it. So I had to manually add mmd_all_letters.txt with this content:
But after that the condition letterText text is "$" worked for me. The variable is increased by 4 and progress bar changes when I add $ to the password.
You can actually get rid of the txt file and AJAX, just store all letters in a text variable. And no need to separate letters with ";", use mid(allLetters, loopindex,1)