MacBook says iPhone password is incorrect

I'm trying to set up iCloud Password & Keychains on my macbook. I click "Sync this mac" and then follow the steps up until it asks me to enter the passcode I use for my iPhone, I enter the correct 4-digit passcode but it says it's incorrect. I haven't changed my passcode for maybe at least a year or so so I'm not sure what's going wrong. I'm not sure how to fix it. /: