We construct infinite-dimensional R-matrices that generalise the relativistic scattering of massless modes with the same chirality on $AdS_2$ near the Berestein-Maldacena-Nastase vacuum. We show that the infrared limit of the R-matrices reproduces finite-dimensional scattering of massless modes on $AdS_2$, from which the R-matrices borrow modified braiding unitary. We also prove that the R-matrices enjoy an infinite-dimensional symmetry superalgebra that embeds that of $AdS_2$. Finally, we verify that the R-matrices are also invariant under crossing symmetry.