They can’t, and some douche bags here are looking to start WWIII.
Only 50% of their reserves have been frozen. They have dollars to pay. Putin is just playing games like a typical deadbeat.
“How the heck are Russians supposed to pay in non-rubles, when their USD reserves have been frozen seized? ”
That is their problem.
They could sell something, but most of the World is scrambling to buy whatever Russia is selling, from anywhere except Russia.
They could borrow to cover their payments, but no one wants to lend to them, and many are legally banned from lending to Russia. Their credit rating is now junk or near junk, so any loans they do get will cost an arm and two legs.
They could try to steal the money, but that is not working out for them either.
The bottom line is that Russia is not going to have enough dollars to service its debt, without sanctions relief. They are going to default, on one bond after another, over the coming months.
Capital and talent are trying to flee, and neither is likely to return, probably for years.