dnd 5th – How does multicasting affect Eldritch calls with level prerequisites?

Only your warlock class counts for prerequisites.

In your study of occult traditions, you have uncovered Eldritch invocations, fragments of forbidden knowledge that permeate you with a permanent magical ability. A required level is your level in this class..

Other elements, such as Cantrips, depend on the general level of your character, but not invocations.