SIYI FT24 - 9.2.2 Receiver and transmitter not bound.

FT24 User Manual V1.1
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8.2 External (Radio) Module
FT24 transmitter works with FM30 radio module and other external third-party
radio modules. R9M protocol is pre-configured in FT24 transmitter. It supports
adjusting settings, monitoring status. For third-party radio modules, please use
PPM / S.BUS connection.
8.2.1 PPM / S.BUS Mode
Under S.BUS / PPM mode, external module outputs signal through the pins
below.