  The neutron star (NS) low-mass X-ray binary (LMXB) the Rapid Burster (RB; MXB
1730-335) uniquely shows both Type-I and Type-II X-ray bursts. The origin of
the latter is ill-understood but has been linked to magnetospheric gating of
the accretion flow. We present a spectral analysis of simultaneous Swift,
NuSTAR and XMM-Newton observations of the RB during its 2015 outburst. Although
a broad Fe-K line has been observed before, the high quality of our
observations allows us to model this line using relativistic reflection models
for the first time. We find that the disk is strongly truncated at
$41.8^{+6.7}_{-5.3}$ gravitational radii ($\sim 87$ km), which supports
magnetospheric Type-II burst models and strongly disfavors models involving
instabilities at the innermost stable circular orbit. Assuming that the RB
magnetic field indeed truncates the disk, we find $B = (6.2 \pm 1.5) \times
10^8$ G, larger than typically inferred for NS LMXBs. In addition, we find a
low inclination ($i = 29\pm2^{\rm o}$). Finally, we comment on the origin of
the Comptonized and thermal components in the RB spectrum.
