Hardly the new peso notes have been released, or counterfeits were already encountered.
It is the 50 pesos note.
The forgers probably had in mind that the new notes are still a bit unknown so that the public must still get used to them.
But also it might have crossed the mind of the counterfeiters, that 50 peso bills are not always checked.
The counterfeit can be recognized easily because of the poor paper quality and also for the missing safety features.
False 50 peso notes in circulation
A sloppy forgery so, but still you have to be careful and check each received 50 peso banknote for authenticity.