An experimental study of the $etato pi^0pi^0eta to 6gamma$ decay has been conducted with the best up-to-date statistical accuracy, by measuring $eta$ mesons produced in the $gamma p to eta p$ reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the $etato pi^0pi^0eta$ matrix element are consistent with the most recent results for $etatopipieta$ decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the $pi^+pi^-$ mass threshold, the magnitude and sign of which, checked within the framework of the nonrelativistic effective-field theory, demonstrated good agreement with the cusp that was predicted based on the $pipi$ scattering length combination, $a_0-a_2$, extracted from $K to 3pi$ decays.
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