2. That Which Invalidates The Fast And Requires The day To Be Made Up Later Together With An Act of Expiation.

The only act that falls under this category is sexual intercourse (while fasting).

Abu Hurairah ® reported that a man came to messenger of Allah (PBUH) and said: “I am destroyed, O Messenger of Allah!”
The Prophet (PBUH) asked: “What has destroyed you?”
He said: “I had intercourse with my wife (during the daylight) in Ramadan”
The Prophet (PBUH) asked: “Are you able to free a slave?”
He said; “No”.
The Prophet (PBUH) asked: “is it possible for you to fast for 2 consecutive months?”
He said: “No”
The Prophet (PBUH) asked: “Is it possible for you to feed sixty poor people?’
He said: “No”
The Prophet (PBUH) said: “Then Sit”

A Basket of dates was brought to the prophet (PBUH) and he said to the man: “Give this in charity”
The Man said: “To someone poorer than us? there is no one in the city who poorer than us!”
The Prophet (PBUH) laughed until his molar teeth could be seen and said: “Go and feed your family with it”
(Related by the group – Bukhari, Muslim, Tirmidhi, Abu Daud, ibn Majah, annasaaee)

The expiation must be in the above order as mentioned in the hadeeth according to the majority of the scholars.