All of that may be true, but it doesn't detract from the fact that money is money, that workers are waged, and you could accumulate, even if it was extremely hard. It is currently very hard to accumulate money for large sections of the global population, but that doesn't mean that what they are trying to accumulate is money. The Polish state, like any other, traded on an international level with money. Stamps are more interesting, but they share the features of a currency: a general equivalent (albeit restricted in this case), accumulative, and transferable.

The fundamental character of money stayed the same, even if there were restrictions on it, as did the capitalist character of money paid through predominant wage labour. The state still collected taxes (perhaps at a different stage in the production process, though) in money. China also has currency controls, but the renmbini is just as much currency as the US dollar is.

Just as a crime exists in a country (albeit with practical restrictions, i.e. you get thrown in prison), money has existed in every modern country, even the so-called "socialist" ones, with some other restrictions.

Money is only as valuable as the people deem it to be. If everybody has a problem spending it and they willfully create secondary markets simply because there isn't even a reasonable amount of demand, it means the money is worthless and that your labor alone has FAR more value. Digging a ditch for someone for a day for a pair of shoes may not be ideal, but working in a factory that pays you in a currency that allows you to get on a waiting list of 6 months to buy shoes is even more less than ideal.

Money accumulation was easy. Spending money was the hard part. You had to know right people to get access to black markets or to know who to bribe to get stuff out the back door.

I'm not sure you know how money worked in communist countries.

The character wasn't the same, because money was not enough to buy you things. You needed special coupons to buy things, and coupons were distributed by the government using various systems.

So you could have enough savings to buy a new car/fuel/washing mashine or even meat, but unless you had a coupon the money gave you nothing.

For that reason for example used cars were sold for above their original price. You could buy a car for an amount, drive it for a few years, and sell it for a higher price than originally - but you wouldn't be able to buy a new one unless you had a coupon for a new one.

The same with fuel or meat. You could have a ton of savings, but unless you have a coupon, you wouldn't be able to buy meat or fuel to that car.

The coupons were distributed by the government through government companies.