Is expiation obligatory for one who committed the sin of incomplete fornication (without penetration) during the day in Ramadan while fasting, but who did not pray or pay Zakat, despite acknowledging God's Lordship and believing in the pillars of Islam?

Adultery is a grave indecency and a major sin. If it occurs during the daylight hours of Ramadan (definition), its sin is compounded. If the questioner inserted part of his penis without full penetration, this is considered complete adultery, which invalidates the fast and necessitates expiation (kaffarah (definition)). However, if there was contact without penetration that led to ejaculation, then the day must be made up (qada'), and the Maliki school of thought holds that expiation is obligatory. If no ejaculation occurred, then there is nothing due except repentance. The questioner has made sincere repentance, and we ask Allah to forgive him.