After downloading the extension, make sure to refresh the youtube page. If still not working you can try turning it on and off or go to its setting and tick ad blocking.
Yeah, as I said in the vid it's easier to buy an Invideo plan with the link, but still you can create enough accounts to remove the watermark from the whole video
let me save you some time...he recommends paying for Invideo. period. and the 'discounted' invideo plan he recommends isn't 'discounted' at all...just the regular price if you pay for Invideo using the yearly plan.