Ipad won't accept my Iphone password

I just bought an Apple Watch 8 & want to pair it with my Ipad. There is an "Update Apple ID Settings" on the Ipad that it wants me to complete. It asks for my AppleID which I enter & it accepts. It then asks for my Ipad passcode - which I enter & it accepts. It then asks me for my Iphone passcode which I enter - & it tells me it's not correct. I have my Iphone in my hand & it is correct. Why won't it accept it?