What is the ruling on the money in my possession, and how do I repent, knowing that I paid off my debt to my creditors with haram money (from an online business that later turned out to be impermissible) without their knowledge of the source of the money?

The basic principle regarding repentance from illicitly gained wealth is to dispose of it. However, if the earnings came from a business whose unlawfulness you were unaware of, and it was not taken from anyone without their consent, then you are not obliged to dispose of it. "So whoever receives an admonition from his Lord and stops, he may have what has already passed, and his affair is to Allah." But if he was aware of its unlawfulness, then he must dispose of the riba by giving it in charity or spending it on good causes.