How to submit response for Google Invisible reCaptcha?

Question

I'm trying to log into website like this: https://google-invisible-captcha-m2.magento-demo.amasty.com/customer/account/create/

It is easy to get the site key info:

        require([
            'Amasty_InvisibleCaptcha/js/model/am-recaptcha',
    ], function (amRecaptchaModel) {
            amRecaptchaModel.setConfig({
                "formsToProtect": "form\u005Baction\u002A\u003D\u0022customer\u002Faccount\u002Fcreatepost\u0022\u005D,form\u005Baction\u002A\u003D\u0022customer\u002Faccount\u002FloginPost\u0022\u005D,form\u005Baction\u002A\u003D\u0022newsletter\u002Fsubscriber\u002Fnew\u0022\u005D,form\u005Baction\u002A\u003D\u0022contact\u002Findex\u002Fpost\u0022\u005D,form\u005Baction\u002A\u003D\u0022customer\u002Faccount\u002Fforgotpasswordpost\u0022\u005D,form\u005Baction\u002A\u003D\u0022review\u002Fproduct\u002Fpost\u0022\u005D,form\u005Baction\u002A\u003D\u0022customer\u002Faccount\u002Fresetpasswordpost\u0022\u005D,form\u005Baction\u002A\u003D\u0022checkout_payment_captcha\u0022\u005D",
                "isEnabledOnPayments": "1",
                "checkoutRecaptchaValidateUrl": "https://google-invisible-captcha-m2.magento-demo.amasty.com/default/amcapthca/checkout/validate/",
                "invisibleCaptchaCustomForm": "-1",
                "recaptchaConfig": {
                    "lang": "hl\u003Den",
                    "theme": "light",
                    "badge": "bottomleft",
                    "sitekey": "6Lck67wUAAAAAPsiz1Y59OrqrpzPcF_ydn40uZhJ",
                    "size": "invisible",
                    "isInvisible": true                },
                "reCaptchaErrorMessage": "Prove you are not a robot"
            })
    });

Then I use 2captcha to get the answer_key successfully. But, I can't figure out where to post the answer key. Any ideas are welcome!