  Recent results from the intensity frontier indicate the tantalizing
possibility of violation in lepton flavour universality. In light of this we
revisit the minimal phenomenological $Z'$ model taking in account both
vectorial and axial-vectorial flavour violating couplings to the charged
leptons. We make a systematic study to identify the minimal framework that can
simultaneously explain the recent results on anomalous magnetic moment of muon
and electron while remaining in consonance with $R_{K^{(*)}}$,
$B^0_s-\bar{B^0_s}$ mixing and angular observables in the $B^+\to K^{+*}
\mu^+\mu^-$ channel reported by the LHCb collaboration. We demonstrate that the
neutrino trident data imply a further ${\rm SU(2)}_L$ violation in the leptonic
couplings of the exotic $Z'$.
