This can only be negotiated by both parties, and there is no objective benchmark to measure it.

It is best to negotiate in advance how to divide the profits after deducting related expenses. In fact, it is equal to your joint investment. He shares in capital, and you share in technology and manpower. This is an equity solution, and the risks are shared.

If you don't want to go to so much trouble, you can tell him to lend you the money. You pay him at a fixed interest rate, so that you can have all the profit distribution rights. This is the way to solve the creditor's rights. He accepts fixed risks, while you have complete control over business activities.