So, apparently the U.S. is blocking Russia from accessing funds in American banks to deal with its debts. They were allowed to use some of it before but not anymore since the tensions flared up. Now they're really in a tough spot.
It’s not like the U.S. just decided to take Russia's money for no reason. This has been frozen due to sanctions. They initially had some access to their funds, but once things escalated with the EU, that got cut off. So now it’s all just sitting there.