My iPad and iPhone won’t pair up

Bluetooth pairing an iPhone and a Mac or an iPad is not supported. 

If you are attempting to use Handoff/Continuity or AirDrop, that does involve Bluetooth but the devices are NOT paired; Bluetooth just needs to be on and the devices in range of each other. The following may help with Handoff/Continuity issues: Use Continuity to connect your Mac, iPhone, iPad, and Apple Watch - Apple Support

Also see Share files between your Mac and Bluetooth devices - Apple Support

And see the information in: Bluetooth: Why can't I pair my iPhone or … - Apple Community

You cannot directly connect your iPad and iPhone via bluetooth pairing.

What exactly are you attempting to do by connecting your iPad and iPhone?

Axel F.