Extra Invocation as Feat for Warlock?

[bid]

There are a couple that have Pact requirements or spell requirements. And I'm AFB but I recall them saying level, not warlock level. And with something like this I find it's best to be explicit.

Anything in the Classes chapter uses class level, as it assumes you are single-classed.
MC assumes you use each of your classes features independently and separately, as if your other class levels didn't exist.

Maybe you want your wizard 1 / cleric 16 to cast wish, but it's a big no-no.