504 - Vocabulary Builder

I downloaded this app like 2 minutes ago tbh but i have some questions: 1: is there like a premium that you have to pay for? Because I read all the reviews (i like reading reviews for some reason) and some of them complained about premium and I downloaded it expecting to see premium or something but it just said you are already premium so I'm confused on that, 2: the words/lessons, how is words like legend, amend, resign, etc in the last/hardest(????) lesson and words like qualify, abandon, oath, etc in the first/easiest(????) so I'm really confused

Very excellent practice! Im not a english person so this helps me a lot by learning all these words and the sentences that included words that are previous lesson practice.