What should someone do who fasted 30 days believing they had reached Ramadan, but then it became clear to them that they began their fasting 11 days after Ramadan?

Whoever started fasting after eleven days of Ramadan due to an excuse, what he fasted of Ramadan is valid and sufficient. And what he fasted after the month is also sufficient and fulfills the obligation according to the general opinion of scholars. However, he must make up one day because his fasting included the day of Eid, and fasting on that day is not permissible, unless Ramadan in his country was twenty-nine days, in which case he is not required to make up any day.