I found solution for my keyboard... When it pops out to put PIN just tipe 4 digit number and click connect and then press the same 4 digit PIN code on your bluetooth keyboard and press enter/return
Hope you found it useful. Please let me know.
Thank you very much for your support, my keyboard is Brand Genius LuxePad 9100 and the indications you comment worked.
Previously, to connect my keyboard when adding bluetooh devices, I had to wait for an 8-digit code to be displayed on the screen and I had to type this code on the Genius keyboard to match it.
I don't know why at some point the 8-digit code was no longer displayed on the screen and could not be set.
Now with the solution that you tell me, just look for the device, then when you ask for the pairing code you have to enter the sequence 1234 on your computer and at the same time on the keyboard the same sequence 1234 and ready to work perfection.
Greetings from Quito - Ecuador.