Kaffaarah for having intercourse with one's wife while fasting in the month of Ramadhaan

Q: About 8 years ago, I had sexual intercourse with my wife while fasting in the month of Ramadaan. I didn't know that time if this was a violation or haraam or if there is any kaffara that needs to be paid. Later I have realized that I might've made a mistake or committed a sin. So I would like to ask what shall I do now? Is there any kaffara that needs to be paid r just ask forgiveness from Allah?