You should be able to choose a Historic deck. Hit the drop down menu under "Challenge Match" and make sure that you have 60 card deck selected.
This thread was added on October 24, 2019, with posts from WotC_Lexie.
Yuuuuuuuuuuuup it's a bug. We're investigating and will keep folks updated!
CAn I get Paid as an external ressource :grinning: you know ... 4-5 mythic wild hehe
No, but I'll DM you a code for something else. :slightly_smiling_face: