  We look at the mass distribution of the $D_s^+ \pi^-$ in the $B^0 \to
\bar{D}^0 D_s^+ \pi^-$ decay, where a peak has been observed in the region of
the $D^*_s \rho$, $D^* K^*$ thresholds. By creating these two channels together
with a $\bar{D}^0$ in $B^0$ decay and letting them interact as coupled
channels, we obtain a structure around their thresholds, short of producing a
bound state, which leads to a peak in the $D_s^+ \pi^-$ mass distribution in
the $B^0 \to \bar{D}^0 D_s^+ \pi^-$ decay. We conclude that the interaction
between the $D^*K^*$ and $D^*_s\rho$ is essential to produce the cusp structure
that we associate to the recently seen $T_{c\bar{s}}(2900)$, and that its
experimental width is mainly due to the decay width of the $\rho$ meson. The
peak obtained together with a smooth background reproduces fairly well the
experimental mass distribution observed in the $B_0 \to \bar{D}^0 D_s^+ \pi^-$
decay.
