I need to invite a current contractor to complete a W9 but the invite button in the tutorial doesn't come up. Is there another way to do it?

The requirement is to have a signed w-9, signed under penalties of perjury as it says on the form

can't do that in QB

download a w-9 they are free, hand it to them and get it filled out

you should have that before you ever do business, you do not want to get involved with backup with holding taxes