ENUBET: the first monitored neutrino beam

The main source of systematic uncertainty on neutrino cross section measurements at the GeV scale originates from the poor knowledge of the initial flux. The goal of the ENUBET project is to cut down this uncertainty to 1\% by monitoring the charged leptons produced in association with neutrinos, through the instrumentation of the decay region of a conventional narrow-band neutrino beam. In this contribution we discuss the final design of the horn-less beamline, that allows for a 1\% measurement of $\nu_e$ and $\nu_\mu$ cross sections in about 3 years of data taking at CERN-SPS using ProtoDUNE as far detector, together with the particle identification performance. We also present for the first time the impact of the lepton monitoring in the reduction of the hadroproduction systematic on the neutrino flux. Finaly, we give an overwiev of the current status of the final demonstrator to be tested with charged particles at CERN in October 2022.