Ref. No. 41/988
In the name of Allah the most Gracious the most merciful
The answer to your question is as follows:
Yes, having sexual intercourse in the state of fast knowingly invalidates the fast, and it leads to both Qaza and Kaffarah. In case it is done unknowingly then fast does not break.
ومن جامع او جومع او اکل او شرف غذاءا او دواءا عمدا قضی وکفر ککفارۃ الظہار (کنزالدقائق ص 68)
And Allah knows best
Darul Uloom Waqf Deoband
This answer was collected from the official website of Darul Uloom Deoband Waqf. The institution is based in India and the answers are provided in accordance to the Hanafi Fiqh.