The v2 API is now dead.

There is now the v3 internal, undocumented API used by the front-end site, which according to the site owner is unstable but can be used if one desires.

It no longer requires a token, and you can search for a song like such at the time of writing ("q" searches both title and lyrics):

https://www.guitarparty.com/api/v3/core/search/?format=json&q=jolene

And then query the song by its ID, which in this case is 5:

https://www.guitarparty.com/api/v3/core/songs/5/?format=json

More API paths can be found on https://www.guitarparty.com/api/v3/core/