- If a song you have uploaded doesn't work anymore, please retry a bit later, if even retrying later doesn't work you can open a support request in the support forum.
- If a song you have followed or favourited doesn't work anymore it might be a federation issue.
If you are in case 2 there isn't much we can do.
By virtue of how the fediverse works, the content is hosted by various instances and servers owned by unrelated entities. This guarantees that no one is in control of everything and you can rely on who you trust for the service, but as no one is in control of everything a content might disappear or a server might become unavailable at any time.
music.inlinestyle.it will notice when a content becomes unavailable, but that takes time (to ensure it doesn't remove content that is just temporarily unavailable due to technical issues) and in the meanwhile the content is listed but won't work.
It's a little bit like a search engine like Google. Once google has indexed a webpage, it will return you that page as a result even if when you click on it you will get an error that the page or the server don't exist anymore. This is because it will take time for Google to notice the webpage doesn't exist anymore and decide that it makes sense to just remove it from its index. That's how the fediverse works too.