I am a Frsky and Crossfire user s I am not familiar enough with spectrum to be sure how to help. Most RX only need 3 wires to make the basics work, +5 volts, Ground, and the control signal wire. Once Betaflight is PROPERLY configured in Configuration/Receiver section you can then test it on the bench with props off. You may want to watch this Bardwell video to get a flavor of what to do. Perhaps some of the spektrum users can chime in with better advice if this doesn't help
You also might want to see if this simple google search yields anything that could help you out.