What is the ruling regarding a husband having intercourse with his wife during the daytime in Ramadan while traveling, out of ignorance of the ruling, 15 years ago?

If a fasting person has intercourse with his wife during the daytime in Ramadan based on an interpretation [of the law], then expiation (kaffarah) is not obligatory for him; only making up the fast (qada') is obligatory, along with a kaffarah for delay if he does not make up the fast within a year. This kaffarah is 750 grams of the staple food of the land for each day. As for a traveler, if he enters a country where he has a wife with whom he has cohabited, his travel ends, and he becomes like a resident. It is obligatory for a Muslim to learn the rulings of his religion.