Subaru BRZ 2017 Owner's Manual page 146

1-7. Safety information
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When installing a child restraint system (without a lock-off) using a
seatbelt
You need a locking clip to install the child restraint system using a seatbelt.
Follow the instructions provided by the manufacturer of the system. If your
child restraint system does not provide a locking clip, we recommend that
you contact any authorized SUBARU dealer or repairer, or another duly
qualified and equipped professional.
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When installing a child restraint system with ISOFIX rigid anchors and
a top strap
Depending on the child restraint system's size and shape, if the child
restraint system is installed to the fixing bars first, it may not be possible to
attach the top strap to the anchor bracket.
In that case, first temporarily attach the top strap to the anchor bracket,
install the child restraint system using the ISOFIX rigid anchors and then
tighten the top strap.
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