I say, and with God's success: The Sunnah of Fajr is not obligatory in the sense that it must be made up; because making up is only for what is obligatory. However, if one misses the Fajr prayer, it should be made up along with the Hadith of the night of travel. Additionally, for one who has missed the Sunnah of Fajr, they can pray two voluntary rak'ahs for the sake of Allah, in order to attain the reward for what they missed from the reward of the Sunnah of Fajr. And Allah knows best.