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I don't have any experience with Flysky im afraid but most RX's ive used give you some form of indication when they successfully bind to a TX. Usually, there's a flashing LED when in bind mode that goes solid when it binds with the TX..something like that.
I also have little experience with beta flight as I generally use Cleanflight but i believe they are very similar
You need to configure the FC so it knows it will be connected to a serial RX and tell it which port that data will be on.
First step is to get the "ports" section in betaflight configured. From what i see on the net, your FC has UART2 dedicated to serial RX's so when you have selected "Serial RX" under the UART2 section in ports ( Please double check with your FC manual) Im telling you what i think here NOT what i know!!!
When the ports section is configured correctly you can go to the main configuration page and select the serial protocol for your RX . Once done dont forget to save and reboot the FC
Good luck