Russia has entire planet delivering weapons to Ukraine so maybe they should do something about that instead of trying to flex on one country which isn't giving weapons to Ukraine
You sound so American State Department... the whole world has Russia under sanctions, which means the US and her bitches.
A couple of unscrupulous countries are making money, that is quite normal but unless Serbia wants to be the US or perhaps France and openly declare friendship with Russia and supply their enemies with weapons in the shadows to make good money, then Serbia needs to really think about what it wants.
Betray Russia and jump into bed with the US and EU... you will still lose Kosovo and any self respect and they will use you like a sheep in a small Australian town.
The way any end-user contract works
If you sell something to someone with a contract that states they are not allowed to sell that something on to anyone else without your permission then if they break that contract by actually doing what they appear to be doing they owe you some more money... at the very least do that.
But no, you claim past actions of Russia means it is OK to produce ammo and weapons for nazis to kill Russian soldiers and civilians... not to mention these companies buying from you that are no doubt making an enormous mark up on what you sold them for when they sold them to the US to provide them to Kiev... they are likely making 100 times more than what you got for making them but I am sure that is OK too.