  Flat spectrum radio quasars (FSRQs) constitute a class of jetted active
galaxies characterized by a very luminous accretion disk, prominent and rapidly
moving line-emitting cloud structures (Broad Line Region, BLR), and a
surrounding dense dust structure known as dusty torus. The intense radiation
field of the accretion disk strongly determines the observational properties of
FSRQs.
  While hundreds of such sources have been detected at GeV energies, only a
handful of them exhibit emission in the very-high-energy (VHE, E $\gtrsim 100$
GeV) range.
  This study presents the results and interpretation derived from a cumulative
observation period of 174 hours dedicated to nine FSRQs conducted with the
MAGIC telescopes from 2008 to 2020. Our findings indicate no statistically
significant ($\geq$ 5 $\sigma$) signal for any of the studied sources,
resulting in upper limits on the emission within the VHE energy range.
  In two of the sources, we derived quite stringent constraints on the
$\gamma$-ray emission in the form of upper limits. Our analysis focuses on
modeling the VHE emission of these two sources in search for hints of
absorption signatures within the broad line region (BLR) radiation field. For
these particular sources, constraints on the distance between the emission
region and the central black hole are derived using a phenomenological model.
Subsequently, these constraints are tested using a framework based on a
leptonic model.
