Moksa means liberation. In other words, Moksa is Enlightenment.

What I found out is that there is one mandatory requirement to attain Moksa: wanting it more than anything else. There are many various paths, all of them are viable, none of them will liberate anyone who doesn't want liberation more than anything else.

In the words of Sri Sankaracarya, in his book Vivekacudamani (The Crest-Jewel of Discrimination), translated by Swami Turiyananda:

(11) Right action helps to purify the heart, but it does not give us direct perception of the Reality. The Reality is attained through discrimination, but not in the smallest degree even by ten million acts.

(27) Longing for liberation is the will to be free from the fetters of ignorance -- beginning with the ego-sense and so on, down to the physical body itself -- through realization of one's true nature.

(31) Among all means of liberation, devotion is supreme. To seek earnestly to know one's real nature -- this is said to be devotion.

(51) Children may free their father from his debts, but no other person can free a man from his bondage; he must do it himself.

(54) A clear vision of the Reality may be obtained only through our own eyes, when they have been opened by spiritual insight -- never through the eyes of some other seer. Through our own eyes we learn what the moon looks like; how could we learn this through the eyes of others?

(55) Those cords that bind us, because of our ignorance, our lustful desires and the fruits of our Karma -- how could anybody but ourselves untie them, even in the course of innumerable ages?

(56) Neither by the practice of Yoga or of Sankhya philosophy, nor by good works, nor by learning, does liberation come; but only through the realization that Atman and Brahman are one -- in no other way.

(59) Study of the scriptures is fruitless as long as Brahman has not been experienced. And when Brahman has been experienced, it is useless to read the scriptures.

(62) A sickness is not cured by saying the word "medicine". You must take the medicine. Liberation does not come by merely saying the word "Brahman". Brahman must be actually experienced.

(182) I tell you this: Have desire for liberation alone, not for anything else. Be resolute for liberation. …

(196) The seer, beyond all qualities, all actions -- the blissful Atman -- has taken this state of being "I" through ignorance only. It is not real. When ignorance comes to naught, it does not remain.

(223) This is the cause of liberation from the world -- the consciousness, the knowledge of the non-separateness of the self from the Supreme. By this knowledge, one attains that Bliss Eternal.

Hare OM!