What is the ruling on a company that prints designs on its products dealing with intermediaries who create their own online stores to display their hypothetical designs on the company's products, such that the amount paid by the customer goes directly to the company's account, and then the company pays a commission to the intermediary? And if that is not permissible, how can it be corrected Islamically?

The real seller is the company that sets the terms of sale and receives the price, even if the store is in the name of the intermediary. The intermediary's job is to design and promote the product, and their contract is with the company, not with the customers. Their profit is a known commission from the company. A salam (forward sale) is permissible if it is for a described item in obligation, and the price is paid in full at the time of contracting.