Charge music on Fioo M11

Hello, I am writing for help on how to load songs on my Fiio M11.
Until now, I have listened to the songs by connecting to Tidal (Never being able to listen to the songs without being connected to the network, but that’s another matter).
I connected the Fiio M11 to the Macbook, I can see the contents, I tried to bring the mp3s to the Fiio in the Music folder, I see them but when I enter the M11 application to listen to them, I always see only the demo song that was loaded on the time of purchase.
What am I doing wrong?
Thanks in advance for the help that will come.
Best regards