I have the kit radio drotek, sik based ( https://drotek.com/shop/fr/drotek-parts/795-kit-radio-telemetrie-433-915-mhz.html ) . They connect each other but no serial connection. I tried to reverse RX with TX but no problem was solved.
Are you using USB or UART?
Try to guess…!
After a day in lab, I found a solution…
Sorry I meant, “do you have the same problem with USB”?
Usb is ok,the problem was with uart. Some FTDI I/O was high when the usb is not plugged. I found a solution changing a settings on FTDI chip.