  A great portion of the cataclysmic variable population, between 40% and 70%,
is predicted to be made up of period-bouncers, systems with degenerate donors
that have evolved past the period minimum. However, due to their intrinsic
faintness, only a few of these systems have been observed and confidently
identified so far. We have searched for X-ray emission as a proof of accretion
in order to confirm period-bounce cataclysmic variables. In a dedicated
XMM-Newton observation of the period-bounce candidate SDSS J151415.65+074446.5
we discovered X-ray modulation at the binary orbital period confirming it as an
accreting system. The X-ray light curve and the X-ray spectrum display
characteristics of magnetic Polar-type systems allowing for the first time the
determination of the X-ray luminosity and mass accretion rate for this system.
Catalog data from eROSITA on the SRG satellite for V379 Vir and SDSS
J125044.42+154957.4 allowed a first look into the X-ray behavior of
period-bounce candidates with this new all-sky instrument. From the eROSITA
measurements the X-ray luminosity and mass accretion rate were determined for
the first time for SDSS J125044.42+154957.4, and the earlier result for V379
Vir from XMM-Newton was confirmed. All three cataclysmic variables with a
magnetic white dwarf and very low-mass donor studied in this work present
evidence for X-ray emission at a similar level of $L_{\rm x}\,{\rm [erg/s]}
\approx 10^{29}$, which, together with the detection of X-ray orbital
modulation in two of them, V379 Vir and SDSS J151415.65+074446.5, unambiguously
proves the presence of accretion in these systems. The detection of these
period-bouncers at faint X-ray luminosity levels with the all-sky X-ray survey
eROSITA offers new prospects for the identification of additional
period-bouncers, providing impetus for theoretical studies of binary evolution.
