So, if a hero has upgraded destiny (+1 on talent), we can't use him. I upgraded a new scull knight to the required level but I can't use him
Nick : klemits
OS : Android
I didn't test that my self but if your sk devo lvl180 then you can use it for exchange skills lvl didn't matter for exchange.
Make sure your hero isn't on any team you use ( dungeon/ lava / labyrinth/ forgotten trial / totam / LBF... etc )
Also remove the crests/ insignia/ pets from your sk
And make sure he isn't locked.
Imo the higher lvl or skills isn't a problem for exchange successful.