Is performing ablution thoroughly a Sunnah or an obligation, and does not performing it thoroughly invalidate the ablution?

Performing ablution thoroughly, which means covering the limbs with water so that it flows over them, is a recommended act (mustahabb) because Allah erases sins and elevates ranks through it. It is also an obligatory act (wajib); without it, ablution is not sufficient, prayer is invalid, and it must be repeated.