As a strategy to persuade Russia to end its war with Ukraine and pull its forces back to Russia proper the NATO/EU sanctions have been an abysmal failure.

That does not mean they have been non-impactful. Quite the contrary, even Russian media is acknowledging that the sanctions are biting, as this discussion of ruble exchange rates in Kommersant illustrates:

The exchange rate of the dollar rose sharply in the Russian market. As a result of trading on Wednesday, the US currency exchange rate amounted to 60.17 rubles / $, which is 1.72 rubles. higher than Friday's close. With the completion of all tax payments, the market faced a shortage of foreign currency supply, the demand for which grew against the backdrop of new sanctions against Russia.

Note the phrase “the market faced a shortage of foreign currency supply”. When countries run out of foreign currency reserves, their ability to import essential goods drops to zero—no foreign currency means no way to pay. Kommersant’s currency analysts are stating outright that Russia is confronted with a lack of essential foreign currency reserves.

Even though the ruble is still stronger now than before the war began, the dollar’s slide against the ruble bottomed out back in July, and the dollar has been steadily strengthening ever since. A stronger dollar/weaker ruble increases Russia’s need for foreign currency—foreign currency it apparently does not have, at least not on a reliable basis.

This doesn’t mean the sanctions regime is going to force Putin to back down any time soon. It does mean the Russian economy is continuing to navigate some very rough and treacherous waters.