How do you use this? – Video to mp3 converter - convert video to audio & music extractor and music player and mp3 trimmer Review

I don’t understand how to use this app. Someone recommended this to me and every time I press convert to mp3 it just says restricted or check with mp3 url. WHAT DOES THAT MEAN?!?!?!
Review by SkyeStar44 on Video to mp3 converter - convert video to audio & music extractor and music player and mp3 trimmer.