What is the ruling on taking a fixed monthly percentage, not subject to increase or decrease, in exchange for providing funds for investment?

It is permissible for one person to give another a sum of money to invest in exchange for a known percentage of the actual profit, such as half or a third. It is not permissible for the owner of the money to have a fixed guaranteed amount or a percentage of the capital without bearing any loss. If a known percentage of the profit is agreed upon, then it is permissible to pay a specific monthly amount on account, and then the accounting is done when the profits are divided.