Wow, I totally didn’t see those. Much too small and low-contrast, they are basically invisible on a smartphone.

I'm not seeing the letters. I see the numbers and vaguely knew enough about chess to know which way the numbers go. Honestly, I really only know about the board location designations because of the puzzle under the word scramble in the paper that asked you to accomplish something on the example chess board. The answers to the previous challenge were written (upside down to prevent accidental spoilers) in the standard(?) chess notation.

I did not see those markings at all - nor did I see the label indicating the square to jump to, until quickthrower2's explanation cued me to look for it!

(I see now that the target-square notation is much more prominent if you stretch the window horizontally, but I habitually use portrait-mode windows, where it's very small.)