Lock roster on Sleeper

Hey everyone,

So I am having trouble collecting league dues from some of my league mates. It was my fault, I waited this long to ensure we were mostly in the clear with covid, but I digress.

Do you know how to lock a roster on Sleeper? I don’t want them to be able to make any roster moves or waiver claims so I can force their hand. If you can’t do that, do you have any other ideas?