The destruction caused by foreign incursions, civil wars, banditry, piracy and pestilence, and depopulation of the countryside, had resulted in a significant decrease in agricultural production, while the military forced the IRS needs to be more oppressive. Compounding the crisis intervened a heavy monetary debasement and progressive who helped bring about a huge increase in food prices.
To give an idea of this vertiginous decline in the purchasing power of the currency, we just have to think about the fact that in Egypt, in the 1st and 2nd century AD, the price of a measure of wheat was fixed around 7-8 drachmas, at the beginning of the 3rd century ad had risen to 20 drachmas and at the end of the century had reached even 120000 drachmas.
They were now only minted copper coins or with a minimal amount of silver; those who still had old coins with high percentages of gold or silver was hidden. There were even strikes of money changers/exchangers who refused to change at the same price as the old and the new coins, since the latter, containing a minor amount of precious metal, in fact were worth much less.
For example, an Egyptian Papyrus of 260 d.C. gives the news that the money changers in the city of Oxyrhynchus had closed its doors and had refused to accept and change the currency issued by Imperial Mint. In many parts of the Empire he returned even to barter, or premonetaria economy: even the taxes were paid by peasants in agricultural products and animals.