MuseScore Pro | MuseScore

You have paid to take out a MuseScore Pro subscription to the score sharing website MuseScore.com. That Pro subscription allows you to download non-public domain scores. It has nothing to do with the MuseScore notation editing software obtainable free (no cost) from here musescore.org/en/download. There is no way to pay for the MuseScore software and no paid for facility to upgrade its facilities. Upgrades come for free as they are developed.

See musescore.org/en/faq#faq-20239

And musescore.org/en/faq#faq-20657

If you realise you don’t want the Pro subscription you may also want to look at this FAQ as well musescore.org/en/faq#faq-314712