  Interacting dark energy models have been suggested as alternatives to the
standard cosmological model, $\Lambda$CDM. We focus on a phenomenologically
interesting class of dark scattering models that is characterised by pure
momentum exchange between dark energy and dark matter. This model extends the
parameter space with respect to $\Lambda$CDM by two parameters, $w$ and $A$,
which define the dark energy equation of state and the strength of the coupling
between dark energy and dark matter, respectively. In order to test
non-standard cosmologies with Stage-IV galaxy clustering surveys, it is crucial
to model mildly nonlinear scales and perform precision vs accuracy tests. We
use the Effective Field Theory of Large-Scale Structure, and we perform
validation tests by means of an MCMC analysis using a large set of N-body
simulations. We find that adding the bispectrum monopole to the power spectrum
multipoles improves the constraints on the dark energy parameters by $\sim 30
\%$ for $k_{\mathrm{max}, B}^{l=0} = 0.11$ $h$ Mpc$^{-1}$ without introducing
biases in the parameter estimation. We also find that the same improvement can
be achieved with more moderate scale cuts and the use of bias relations, or
with the addition of the bispectrum quadrupole. Finally, we study degeneracies
between the dark energy parameters and the scalar amplitude $A_\mathrm{s}$ and
discuss the corresponding projection effects, as well as degeneracies with
other cosmological parameters.
