Shaykh Salih Al-Fawzan [حفظه الله] said:

❝Failing to fast in Ramadan without a [legitimate] excuse is a grave error and a huge crime. Whoever does this must make sincere Tawbah, regret what he has done, never do it again, and never miss another fast. He must also make up for the missed days.❞

[Majmū’ Fatāwá Al-Fawzān, (2/415) | Translated By Musa Shaleem Mohammed]