IPA: /ʌnˈpɒpjʊləli/
KK: /ʌnˈpɑpjələrli/
In a way that is not liked or accepted by many people.
The movie was unpopularly received by critics, despite its star cast.
Unpopularly → It is formed from "un-" (meaning not) and "popular" (from Latin "popularis", meaning of the people) and "-ly" (meaning in a manner). The word "unpopularly" means in a manner that is not favored or liked by the people.
Think of 'not' ('un-') being combined with 'of the people' ('popular') to remember that 'unpopularly' describes something that is not liked by the majority.