First please make sure your RXSR receiver has flashed the correct F.Port PROTOCOL FIRMWARE , download from https://www.frsky-rc.com/r-xsr/
Connection diagram(Please careful weld since the tiny soldering pin)
Betaflight setup: Enable Serial RX for UART2 and select Serial-based receiver for the Receiver Mode, then choose Frsky FPort in the tab list from Serial Receiver provider. Don’t forget to enable Telemetry
set serialrx_halfduplex = ON set serialrx_inverted = OFF save
Please how the F.Port works with the Crazybee F4 v2.0 No RX Version.
Is it possible to use f.port in Crazybee F4 PRO V2.1 and Frsky ARCHER M + receiver?
A 100uF Capacitor should be enough for 3S 300~350mah battery on the Crazybee F4 PRO V2.0 and V2.1, and 2S 300~350mah battery for the V1.0. For batteries larger than the 350mah mark, they recommend using a 220uF or larger capacitor. With the Crazybee F4 PRO V3.0 , they no longer supply a capacitor for this board.