I was stuck on this task and by checking the answer seems like there is an error there:
SIDUGRFBXGARYW is the ciphertext and WCHXOR is a key (from hint). Decrypting it using Playfair algorithm the resulting text should be PLAYFAIRCKRETX and not PLAYFAIRCKRET:
WCHXO
RABDE
FGIKL
MNPQS
TUVYZ
SI DU GR FB XG AR YW
PL AY FA IR CK RE TX
P.S. Really liked your workshop in BuildStuff, cheers!