What is the ruling on working through the website "Merch by Amazon," where the worker designs and uploads T-shirt designs, sets their price, and receives a specific share of the profits for each sale?

There is no objection to a worker agreeing with a website to design a type of clothing, and the website undertaking the promotion of the design and the production of the garment for those who desire it, provided that the worker receives a known percentage of the price, such as five dollars out of every twenty dollars. This is permissible because the worker is a partner with the website in exchange for a known percentage of the price.