Is money gained from investing a small amount in an online earning platform that doubled within four days considered permissible (halal) or forbidden (haram)?

If the profit is a stipulated percentage on the website, then this is a forbidden and void transaction, taking the ruling of a usurious loan. It is not permissible for one partner to have an excess amount of money. However, if the mentioned profit occurred by agreement, then there is no issue with its amount or timing. But the method of investment through the aforementioned website still needs to be considered, and judgment on a matter is a branch of its conception.