How to find find the Callback function 2Capthcha ?

#1
Hello,
I still can't find the Callback function 2Capthcha :(
I read the previous posts but I don't get it ;/

can you show him on this page where to look for him? I don't see anything like that here ___grecaptcha_cfg.clients[0]
one thing i found was a ___grecaptcha_cfg.clients[d] but there is no callback function.

example page where you try to learn it below just click the login and the captcha pop up

https://www.mercadobitcoin.com.br/conta/login/

I am asking for help in learning