how to connect TBS Crossfire Nano Rx
To Flycolor X-Tower F4 FC ?

Wire the Crossfire Nano to the Flycolor X-Tower (the connector highlighted in yellow below) as follows:-

TBS Crossfire Nano     Flycolor X-Tower
GND -----------------> GND pin
5V In ---------------> 5V pin
Ch. Out 1 (TX) ------> RX3 pin
Ch. Out 2 (RX) ------> TX3 pin






Then in Betaflight Configurator:-

1. On the Ports tab ensure that "Serial RX" is switched ON for UART3 and that "Serial RX" is switched OFF for all other UARTs.
   
2. On the Configuration tab, select "Serial-based receiver" for the receiver mode, select "CRSF" for the serial receiver provider, and ensure that "TELEMETRY" is switched ON under the other features section.
   

Thank you very much

Note that I've just updated the diagram and instructions in my post above to make use of UART3 instead of UART1 for the Crossfire Nano. This is because I forgot that UART1 is shared with SBUS and so has a built-in inverter so that won't work with the uninverted signal of the CRSF protocol.

Because of this The telemetry was disconnects after 100 meters, but the rssi remains high?