Corrected invariant mass spectrum for the coherent four-pion photoproduction fitted to the model described by a single resonance and an alternative shape of the non-resonant production given by eq.~\ref{eq:supp_Fnr}. Black error bars represent the statistical uncertainty, the orange band shows the uncorrelated systematic uncertainty, and the boxes show them added in quadrature. ``Prob'' reflects the probability of obtaining the given or a higher $\chi^2/\mathrm{ndf}$ of the fit.