The Dark Arts Archlich Patron for Warlock says that:
At 1st level, when you expend a spell slot of 1st level or higher, you and all that you are wearing or carrying becomes invisible until the start of your next turn, or until you attack or cast a spell.
But Warlock Spellcasting says expending a spell slot like that happens any time you cast a level 1 or higher spell (PHB):
The Warlock table shows how many spell slots you have. The table also shows what the level of those slots is; all of your spell slots are the same level. To cast one of your warlock spells of 1st level or higher, you must expend a spell slot.
Does this mean that the Arcane Invisibility power triggers whenever the PC casts any spell of level 1 or higher, since that expends a level 1 or higher spell slot? (Any spell other than a cantrip).
In other words, if the PC casts a level 1 spell such as hex, does the PC become invisible?
For Clarity on Material: