How do I find the callback function? I cannot find the captcha submission form.

#2
Sometimes there's no submit button and a callback function is used isntead. The function is executed when reCaptcha is solved.

Callback function is usually defined in data-callback parameter of reCaptcha, for example:
Code:
data-callback="myCallbackFunction"
Or sometimes it's defined as callback parameter of grecaptcha.render function, for example:
Code:
grecaptcha.render('example', {

  'sitekey' : 'someSitekey',

  'callback' : myCallbackFunction,

  'theme' : 'dark'

});
Also there's another way to find the callback function - open javascript console of your browser and explore ReCaptcha configuration object:
Code:
___grecaptcha_cfg.clients[0].aa.l.callback
Note that aa.l may change and there can be multiple clients so you have to check clients[1], clients[2] too.

Or just use the script that finds ReCaptcha parameters

Finally all you have to do is to call that function:
Code:
myCallbackFunction();
Or even this way:
Code:
___grecaptcha_cfg.clients[0].aa.l.callback();
Sometimes it is required to provide an argument and in most cases you should put the token there. For example:

Code:
myCallbackFunction('TOKEN');