I don't assume that all critics don't know what they are talking about, but no offense, you did not in fact know the information required to understand Marx's Labor Voucher system.

My bad, that may have sounded a bit agressive. I just mean that I know people on Lemmy tends to have very... polarized opinions of the political literacy of other people they disagree with, and I know that I'm not immune to that either. That's more to show my position on this than to point out something you did specifically.

the USSR did in fact try to abolish "money," but went about it poorly and it failed.

Yep, that exactly my point. Money is kind of central to a complex economy, and the USSR had issues even while still using it.

The USSR planned everything by hand, and still managed to develop rapidly and provide for their people

You may want to look at the opinion of someone like Paul Krugman on that. He makes some interesting parallels in the rapid industrialization of countries like South Korea or Japan and what happened in the USSR before, using the difference between intensive and extensive growth. For him, the gist of it is that authoritarian control of the economy can provide impressive extensive growth (put people to work, mechanize agriculture, provide basic education, infrastructure, etc...), but that once you reach a somewhat prosperous but intermediary state, you need to switch to intensive growth (creating more output value for less inputs) to get to the "next stage", so to speak. He also argues that South Korea and Japan did this, while the USSR never managed and that's why from the 60's onward the economic prosperity of the USSR entered a long period of stagnation.

which aspects of Marx had issues? Do you have any actual examples I can look at?

I mostly disagree with the extreme reductionism of historical materialism, which affirm that the whole of history is the history of the possession of the means of production. That mean that while I understand that the bourgeoisie/proletariat dichotomy as a useful heuristic about social analysis, I don't belive it is necessarily the most useful one in all cases. From there, the notion of the superiority of the "dictatorship of the proletariat" becomes very shaky, so the political theory of action all goes downhill from there. And globally, the whole problem of Economic Calculation make the whole theory of the working of communism I extremely difficult to solve (but to the credit of Marx, this problem would only emerge due to a better understand of market-based economics, half a century later).