I had a wet dream one day in Ramadhaan so I broke my fast out of ignorance of Fiqh (jurisprudential) rulings. Later, I found out that wet dreams do not invalidate fasting. What is the ruling on this?

All perfect praise be to Allaah, the Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

Ignorance of Sharee‘ah rulings drags the Muslim to commit such great violations. For that reason, we often remind Muslims to be keen on seeking Sharee‘ah knowledge and on acquiring it from its correct sources to enable the Muslim to worship Allaah on clear evidence. The Prophet, sallallaahu ‘alayhi wa sallam, criticized the one who is ignorant of his religious teachings. He said: "Allaah hates every arrogant and harsh person who speaks loudly in the markets, sleeps like carrion by night and gets involved in work like donkeys by day. He knows everything about this life and does not know anything about the Hereafter." [Ibn Hibbaan] [Al-Albaani: Saheeh]

You have to repent to Allaah The Almighty of your negligence in acquiring the obligatory knowledge as learning matters which make one's worship valid is an individual obligation for every Muslim. The Prophet, sallallaahu ‘alayhi wa sallam, said: "Seeking knowledge is obligatory for every Muslim." [Ibn Maajah and others]

There is no doubt that having wet dreams on the day of Ramadan does not invalidate one's fasting. After repenting to Allaah for neglecting acquiring knowledge, you have to make up for that day. It is a debt and you cannot be free from liability except by fasting it. The Prophet, sallallaahu ‘alayhi wa sallam, said: "The debt you owe Allaah is worthier of being repaid." [Al-Bukhari and Muslim]

And Allaah Knows best.