Can Only Download Local Files From One PC

[nd1san]

Hello, since I started using Spotify Premium in 2016 and my brother set the account up, I have not been able to load local files onto my phone from any device apart from the old MacBook Air we used to use, which has since been rendered obsolete.

After he made a new account under mine through Premium Family Sharing, he can load local files from his new MacBook Pro, while my original account is still unable to do so.

If anyone knows anything about how to fix this, your help would be greatly appreciated.