There wasn't a lot of what we would consider 'real money'. Thanks to Andrew Jackson dismantling the Bank of the United States, there was a little bit of coined money coming out of the US mints - and a flood of paper notes issued basically by any bank that wanted to do so. Counterfeiting was easy and rampant (would you recognize a $2 note from the Farmers Bank of Denver? IS there a Farmer's Bank of Denver?), discounting was severe (would you gamble on that $2 note for $2 worth of materials or offer $1?) and control was non-existent. But the bank notes were necessary because Congress would not approve issuing Federal paper notes and there just wasn't enough gold and silver to mint enough coin for the size of the US economy (probably the greatest in the world sometime between 1876 and 1890). This is why California (and later Montana, Idaho, the Dakotas and Colorado were so vitally important - as was the rise of a solid, trust-able paper note).
As a result of loose financial control the US suffered a major contraction/expansion cycle about every 8 years. The war brought some stability - massive spending led to steadier economic expansion and the issue of Union 'greenbacks' (printed in green ink on the back side) helped get enough cash into an economy that needed a lot of liquid capital. The South printed a lot of money - a lot more than the Union - but unlike the greenbacks theirs were backed only by patriotism and hope and their value declined under Weimar-like inflation.
The South ended the war with its railroads and factories destroyed, entire cities burned down (Richmond, Columbia, Atlanta), billions of investment in slaves evaporated and with the life-savings of many, having been invested in Southern victory, gone up in smoke. Add in the fact that 250,000 male (worker) casualties came out of a total population of maybe 6 million... and many more people were permanently injured...
The rural South had gotten by on barter for decades - where there is little trade there is little money - and post-war found they had little to sell and no hard cash on hand. All Confederate money was worthless and the rich planters had never had any money - everything was invested in more slaves and more land, or in building fine homes. The big plantations couldn't operate without labor and that cheap labor had run off, so without a cash crop to sell there wasn't anything to sell but land. Enter carpetbaggers...
Part of what the North wanted from Reconstruction was to have Freedmen and poorer whites own and run small farms (40 Acres And A Mule). They'd have modest prosperity as in the North and Midwest and would owe loyalty to Republicans for giving it to them. That would build up a power bloc against the former slave-owners and big plantation owners. But...
Northern farms already produced enough grains and livestock. What the South had to sell before-the-war were VERY profitable cash crops like cotton, tobacco, hemp, rice and indigo (and some sugar, I think). But you cannot profitably raise those crops without a lot of labor, or move them to market without railroads, steamboats and cash. And since cotton rips the nutrients out of the soil you need a LOT of new land (the original reason the South wanted slavery expanded).
So: enter sharecropping, the company store and company scrip to pay the workers, not cash. But... you need a big operation to run those, to clear new land and to grow the big profitable cash crops. Small farms can't do it, can't raise or sell much of anything else and so have no cash on hand (and they must have cash for hardware and anything they cannot grow or make).
Ergo, when the tax-man comes (and he only accepts hard money) they can't pay, either because they ate what they raised (and so could not sell it) or because they couldn't raise high-value cash crops - and so have no cash. This creates no loyalty to the government taxing them and in addition drives a wedge between poorer whites and Freedmen ('They're takin' yer jobs!').
Apologies for the extreme length. I'm not an expert on finance or financial history, so feel free to correct what I got wrong. But the tl;dr is that the South lost almost all pre-war accumulated wealth and entered into an era of having to pay for labor and pay for fertilizer for worn-out soil, an era of very depressed prices for their agricultural products and an era of hard, deflationary money policy (the gold versus silver debate).
@JodelDiplom - the truth is they had no money for taxes because they literally had no money.