how to enable Submit button on callback if recaptcha successful

hi ,everyone,
right now,




I have a very simple form as follows. I want to make it so that the Submit button is disabled, and only enabled after the user has successfully completed the ReCaptcha.
but i failture many times ,whether i completed ReCaptcha or not , i click sumbit ,it enabled

can you help me?thanks
such as ,

after the user has successfully completed the Re C a p tcha.

he will visit https://www.blackhatworld.com

use ReCaptcha V2, all code in 1.php

this is my code:

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davids355 said:

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thanks