Probably an ancient copy from dies in official style, probably mechanically derived from genuine coins.
The reverse is actually of Elagabalus in 219 or Severus Alexander
in 231, and it seems highly unlikely that the mint still had an obverse die of Caracalla on hand and mistakenly brought it back into use two years or fourteen years after that emperor's death!
RIC 378 of Septimius is Eastern, but the reverse of your coin is clearly in Roman style.
Unfortunately the true explanation is simpler: both dies are by Lipanoff, the obv. no. 81 in Prokopov's book, the rev. no. 104 (Severus Alexander
)! I hope you can return it.