I have two questions with regards to how the spell Sleep interacts with the Eldritch Invocation Aspect of the Moon (hereafter AotM) for Pact of the Tome Warlocks from XGtE. I did not separate them into two separate question pages because the second is dependent on the answer to the first.

1. Does Sleep override AotM?

The phrasing of the invocation from XGtE pg. 56 is such:

"You no longer need to sleep and can't be forced to sleep by any means." (emphasis mine)

To me this phrasing sounds like it is specifically referring to means such as the Sleep spell, however I have seen it argued in other places that since Sleep's phrasing is:

"Each creature affected by this spell falls unconscious until the spell ends..." PHB pg. 276 (emphasis mine)

and AotM does not make one immune to the unconscious condition, said Warlock would still be affected. However the phrasing of the spell also uses words like "magical slumber" and "the sleeper". So question 1, is a Warlock with AotM affected by the Sleep spell or not?

2. If a Warlock with AotM is not affected by the Sleep spell, does their current HP count towards the total HP targeted by the spell?

The phrasing of the spell, again from PHB pg. 276 is:

"Roll 5d8; the total is how many hit points of creatures this spell can affect. Creatures within 20 feet of a point you choose within range are affected in ascending order of their current hit points (ignoring unconscious creatures.) Starting with the creature that has the lowest current hit points, each creature affected by this spell falls unconscious until the spell ends, the sleeper takes damage, or someone uses an action to shake or slap the sleeper awake. Subtract each creature's hit points from the total before moving on the creature with the next lowest hit points..."

If the Warlock with AotM has the lowest current HP, and they can't be affected by the spell, does their current HP still subtract from the total targetable HP? Or would the spell instead just skip them and start with the first creature that can be affected with the lowest current HP?

Does Sleep override AotM? No.

Nor does poison, magic dust, or anything. There are no means that will force the character to sleep.

Elves and others immune to the sleep spell, like undead, do not count towards the hp total.

The presence of unaffected creatures does not shield affected ones.

Parsing the sleep spell

Creatures ... are affected in ascending order of their current hit points

Those that can't be affected aren't in this group.

Starting with the creature that has the lowest current hit points, each creature affected by this spell falls unconscious until..

Reiteration of creatures in the group to be considered. Those that can't be affected aren't in the group.

Subtract each creature's hit points from the total before moving on the creature with the next lowest hit points..."

Each creature described in this statement is drawn from the set described by the previous one. So only apply the sleep condition and total subtraction on creatures that are affected.

For sleep spell HP count, Mike Mearls has a sage advice (January 31, 2016) clarifying that elves don't count towards the HP total because of their sleep immunity, so logically the same has to apply to our warlock. Not how I would rule (spells target immune creatures all the time, they just have no effect), but that's the word from the horse's mouth.

You have hit upon a legitimate inconsistency in the phrasing of the unconscious condition. However, the "fey ancestry" attribute of elves says "magic can’t put you to sleep", and this seems to be universally accepted as applying to the "unconscious" state which the sleep spell effects, including in the reference above. Once again this seems logically to have the same intent as the warlock ability.