  Transit Timing Variations (TTVs) can provide useful information for systems
observed by transit, by putting constraints on the masses and eccentricities of
the observed planets, or even constrain the existence of non-transiting
companions. However, TTVs can also prevent the detection of small planets in
transit surveys, or bias the recovered planetary and transit parameters. Here
we show that Kepler-1972 c, initially the "not transit-like" false positive
KOI-3184.02, is an Earth-sized planet whose orbit is perturbed by Kepler-1972 b
(initially KOI-3184.01). The pair is locked in a 3:2 Mean-motion resonance,
each planet displaying TTVs of more than 6h hours of amplitude over the
duration of the Kepler mission. The two planets have similar masses $m_b/m_c
=0.956_{-0.051}^{+0.056}$ and radii $R_b=0.802_{-0.041}^{+0.042}R_{Earth}$,
$R_c=0.868_{-0.050}^{+0.051}R_{Earth}$, and the whole system, including the
inner candidate KOI-3184.03, appear to be coplanar. Despite the faintness of
the signals (SNR of 1.35 for each transit of Kepler-1972 b and 1.10 for
Kepler-1972 c), we recovered the transits of the planets using the RIVERS
method, based on the recognition of the tracks of planets in river diagrams
using machine learning, and a photo-dynamic fit of the lightcurve. Recovering
the correct ephemerides of the planets is essential to have a complete picture
of the observed planetary systems. In particular, we show that in Kepler-1972,
not taking into account planet-planet interactions yields an error of $\sim
30\%$ on the radii of planets b and c, in addition to generating in-transit
scatter, which leads to mistake KOI3184.02 for a false positive. Alleviating
this bias is essential for an unbiased view of Kepler systems, some of the TESS
stars, and the upcoming PLATO mission.
