Set this HTTPS URL as your Default Endpoint in the Alexa Developer Console (SSL Certificate Type: My development endpoint has a certificate from a trusted certificate authority):
https://ytmusic.toldar.com/alexa
Queue is currently empty. Say "Alexa, ask YouTube Music to play..."
Connecting your account unlocks "play my liked songs", "play my supermix", "play my [name] playlist", and "I like this song".
F12 → open the Network tab → filter by browse.browse?... POST request, and copy the Request Headers (or click Copy as cURL (bash)).