Why can't I pair my phone / tablet?

[AC Question]

I'm having some trouble getting my nexus 7 and Z3 compact to pair via bluetooth. They can both see each other and when I select one of them they try to connect and I get a prompt on both screens which contains the same pairing number (I don't have to type anything in, there's just the number with a pair button), however regardless of which one I press pair on first or whether I do it at the same time it doesn't connect. Sometimes it says it failed and other times it just doesn't work. I actually have the same issue pairing my phone to the car - the car comes up with the pairing code and I get the below screen on my phone, but when I press pair it instantly says 'authorization failed' on the car display.

Thanks