That’s a very smart question to ask, as getting this wrong can cause major headaches.
The Safest Method: To avoid all copyright issues, you must only use the audio tracks available within the official Facebook Reels music library when you create your video.
The key is understanding the difference between listening to an audio track and having a license to use it in your video content.
The reason your last Reel was muted is because you used a downloaded audio file, which is a direct copyright infringement. The big creators you see are using popular songs by selecting them from the music sticker or audio tool inside the Reels editor itself. Facebook has already paid for the licenses for that specific library of music, making it completely safe for you to add to your video content without fear of getting a strike. Be aware that Business Accounts often have a more limited selection of popular songs due to commercial licensing, but for a personal or creator account, the in-app library is the correct and safe way to go.
Cheers,
Jeff