Amateur has no negative connotations to me (as a native English speaker from the Midwest US). It's comparable to "hobbyist" or "enthusiast", basically meaning "someone who can do X but doesn't get paid for it". I think a lot of people would be proud to be amateur musicians or amateur athletes, for example, and would have said that no (non-professional) customer would not want to be called an amateur. Just shows you have to be careful!
And the pricing page (https://m3u-editor.com/#pricing) looks pretty good to me - nice horizontal feature matrix, easy to locate buttons...not sure OP wants to use dark patterns like de-emphasizing the free tier. I do agree that the top plan should probably be more than $5/mo.