Work For Hire (contracting) is an essential contract for the livelihood of contractor and contracted. It is clean, clear, cut and dry. MM, the split you are requesting is a completely different contract. To add a ‘split’ phrase would nullify the entire WFH concept as it was meant to be understood and applied in regards to this project. Not to say you don’t deserve more money. There are just better ways to get more $$. The YouTuber who hired you was wise not to so casually enter into an instant business partnership via a clause on a WFH agreement.