Came across this while having the same issue earlier.
I wanted to connect my keyboard to my laptop, got shown a pin ONCE, the just got told to enter the appropriate pin without showing it again... any pin I tried didn’t work. Neither 0000, nor 1234, nor the giant pin on the back of the keyboard, not anything. It just said ‘unable to connect’ or ‘That pin doesn’t work’ or some variation of that.
What I did that resolved my issue was connect the keyboard to my phone, it asked for a pin, I wrote this pin down (hoping the pin was set for the keyboard and not randomly generated) and went through the steps on my phone etc.
Then I tried to connect the keyboard to my laptop again, using the same pin I got from my phone and it works on my laptop now so that’s nice
I’m not sure if that’ll work for anyone else but if you’re desperate it’s worth a try I think 🤷