As an example: php miio-cli.php --ip 192.168.1.123 --token 3XXXXXXXXXXXXXXXXXXXXXXXXXXXXX22 --sendcmd '{"id":1,"method":"get_music_free_space","params":[]}’ Actually I've just wrapped all this long thing into a 1-line script which takes the command and add all this long stuff before it, like #!/bin/b ...

Try to include again as if it were 'new' (but don't exclude before it).
Controller will find existing device (id will not change) and initiate the config.

Need miio (any flavour - php-miio, python-miio, etc.) and available gateway token and IP (token you can look in mihome, at page where you switch on developer's mode). 1. Convert the source mp3 into aac for gateway: ffmpeg -i 18Track.mp3 -b:a 64k tr18a.aac 2. Place converted file into place available ...

Actually it is not mp3, but aac
(have tried mp3 directly, gateway doesn't play it)
64k aac is ok.

(I believe miHome makes conversion via xiaomi's cloud when accept mp3 in application, but I've tried directly uploaded file)