It is well known that dark photons can resonantly convert to normal photons if the effective mass of the photon is equal to the mass of a dark photon. Constraints on dark photons were put from dark-to-normal photon (in both directions) considering the conversion at high-redshift, almost homogeneous Universe. I will discuss the conversion at low redshifts that happens in the inhomogeneous Universe. For this, I use the data from 100 cMpc Eagle simulations. I will apply these results to the model by Pospelov et al [1803.07048], where dark photons are created from the decays of DM axions. This model was proposed as a possible explanation of EDGES anomaly in the 21cm signal. I will show that taking into account late time conversion allows excluding a large part of the parameter space of this model.