The callback can be found here: ___grecaptcha_cfg.clients[0].ba.l.callback
As it's an anonymous function the best way to call it is: ___grecaptcha_cfg.clients[0].ba.l.callback("TOKEN");
Spotify replaced recaptcha v2 with recaptcha v3.
Now you should use the corresponding API method, new v3 sitekey value and also provide additional parameter action=login