  We investigate the emergence of ferromagnetism in the two-dimensional
metal-halide CoBr$_2$, with a special focus on the role of electronic
correlations. The calculated phonon spectrum shows that the system is
thermodynamically stable unlike other Co halides. We apply two well-known
methods for the estimation of the Curie temperature. First, we do DFT+U
calculations to calculate exchange couplings, which are subsequently used in a
classical Monte Carlo simulation of the resulting Ising spin model. The
transition temperature calculated in this way is in the order of 100 K, but
shows a strong dependence on the choice of interaction parameters. Second, we
apply dynamical mean-field theory to calculate the correlated electronic
structure and estimate the transition temperature. This results in a similar
estimate for a noticeable transition temperature of approximately 100 K,
however, without the strong dependence on the interaction parameters. We
attribute this rather high transition temperature to the vicinity of the system
to a paramagnetic Mott metal-to-insulator transition. The robustness of the
transition temperature with respect to the interaction values can be traced
back to the special electronic configuration with five electrons in the
$t_{2g}$ and two electrons in the $e_g$ orbitals, showing a very weak
dependence of the single-particle gap on the Hubbard interaction U.
