Magic Keyboard pairing

I bought a Magic Keyboard (1st generation) from Goodwill. I powered it on and the green light turned on. It showed up on my iPhone’s Bluetooth menu. I tried to pair it and when it asked for the code it kept rejecting it. It said “Pairing Unsuccessful iPhone can no longer connect to "Apple Wireless Keyboard” “Forget this device” I tried pairing to an Android tablet and that said my code was incorrect after multiple tries. Is the keyboard possibly still tied to the previous computer? Do you have to be very fast when typing the code?