Putin has threatened so called unfriendly states to pay in rubles or have its gas supply shut off. It has said it doesn't buy things for free and so isn't going to charitable with its energy.
Europe has kicked against this with Germany saying its being blackmailed by this move. What other choice does Europe has with Russia alone selling about 40% of energy to the world.
No matter what they say in the end you will see that they are buying oil and gas from Russia by rubble, whether openly or secretly. Because they have no choice but to do so. Europe imports 40% of its oil and gas from Russia. Europe will have to spend a lot of time looking for alternative routes and will have to pay higher prices than could be bought from Russia. I wouldn't call selling oil and gas in rubles a blackmail because if everything can be bought with USD then why not rubble? The USD is a country's currency, the ruble is also a country's currency .
They had hundreds of years to generate an alternative to Russian gas and they didn't. All this complacency has produced results and Europe will have to lend an arm to avoid a collapse.