Rampant Inflation destroyed the Roman Economy
From the 3rd century onwards many Roman emperors would debase the coinage, rendering it nearly worthless. A barter economy returned in many places and people struggled to cope with the now heavy tax burden. The Roman state was broke by the time of the barbarian incursions of the 4th-5th centuries.
During the late 2nd and early 3rd centuries AD, the military Severan dynasty debased the Roman coinage in order to expand the military and increase soldiers' pay. By reducing the silver content in the denarius they accidentally caused massive inflation. Many other emperors would copy them during the 3rd century. Studies by archaeologists show that the denarius went from 90% silver to just 5% in the 3rd century. Prices rose at least 1000% in this period.  A series of 4th-century reforming emperors tried to resuscitate the currency with limited success. A fast expanding army and bureaucracy, made to cope with Rome’s now enormous size, required more tax revenue than ever before from the failing economy. In the sources from late antiquity, we know that many Romans were petrified of the now ruthless tax collectors and that increasingly the peasantry was tied to the land to prevent them from absconding. The Roman government still wished to be paid in gold, although ordinary people were effectively using a fiat currency, or else had returned to a barter system. By the 5th century, many Romans were happy to abandon the Empire to Germanic tribes, in the face of unreasonable economic conditions.  Inflation may have contributed to a weak military, instability, and a lack of loyalty to the Empire itself.
The hyperinflation caused by the 3rd-century emperors was effectively slowed by the emperors Aurelian, Diocletian, and Constantine. All three emperors realized that the degradation of the coinage had caused the problem and struck new coins.  Although not all of these attempts were successful, a pure gold coin, known as the Solidus, struck by Constantine I, has become known as the dollar of the middle ages because of its purity. Although inflation was still an issue, the economy did begin to recover. Many historians refer to the early 4th century as the Roman restoration, rather than seeing this period as a downward slide leading to the fall of Rome. The role of inflation in the fall of Rome is often exaggerated. There were many successful attempts to combat inflation. The 4th century was a recovery period.
[P1] Devaluing of the Roman coinage led to rampant inflation. [P2] Rome's economy never recovered [C] The Roman state was weakened by a failing economy
Rejecting the premises
[Rejecting P2 ] The Roman economy did recover in the 4th century