Apple Watch unlock my Mac

Hi everyone!

Recently, I bought my first Apple Watch. Since macOS Sierra (I believe) you should be able to unlock your Mac using your Apple Watch. This feature can be turned on other settings > security & Privacy > general, but I don't see a button to turn it on anywhere. Does someone know how to fix this? I do have 2 step verification and hand-off turned on for that matter.

Thanks in advance!

I am trying to get this work with a (2017) MacBook Air & Apple Watch (series 4)