Icloud pin

Good afternoon,

We purchased an iphone 13 and transferred data easily and are using the phone, however it continues to disconnect from Icloud and asks for a pin that I don't recall ever setting up. I tired a random pin and was able to disconnect the find my iphone lock to send the 11 in as a trade in, now that pin won't work for this issue. Anyone else have icloud issues after switching phones. Never had an issue with it on my 11 until I tried resetting it for trade in, now it won't accept the pin on the new phone. My watch keeps disconnecting too. It's very annoying.