Can we not use units to refresh in Road to Greatness Arena?

I'm not an arena grinder so wanted to try refreshing some champs to pound out this arena faster, but every time I get an error. Is this happening to anyone else or are we just not allowed to refresh for this arena?
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Because I want to...
I'm close to a 6* and if i can get the shards to open a 5* and get a duplicate now that will expedite the process
😂😂😂😂😂
Alot of "ifs" in that statement. Best of luck to you.