I have two domains, a and b, both with reCAPTCHA enabled. I'm using the same codebase for both websites, but the reCAPTCHA implementation works on a but not on b. Here's the setup:

a: The reCAPTCHA keys were created by a friend 2 years ago. The keys are for reCAPTCHA v3, as the site uses grecaptcha.execute.

b: The reCAPTCHA keys were created today, and I used reCAPTCHA v3 for this domain as well.

On b, I get an error:

contact.php:37 Uncaught (in promise) TypeError: Cannot set properties of null (setting 'value')
    at contact.php:37:71
(anonymous) @   contact.php:37
Promise.then        
then    @   recaptcha__en.js:591
(anonymous) @   contact.php:36
Promise.then        
(anonymous) @   recaptcha__en.js:138
(anonymous) @   recaptcha__en.js:195
(anonymous) @   recaptcha__en.js:196
(anonymous) @   recaptcha__en.js:472
(anonymous) @   recaptcha__en.js:196
(anonymous) @   recaptcha__en.js:1132
(anonymous) @   recaptcha__en.js:1142

Here's the client-side code I’m using:

<script src=".js?render=mysitekey"></script>
<script>
    grecaptcha.ready(function() {
        grecaptcha.execute('mysitekey', {action: 'contact_form'})
            .then(function(token) {
                document.getElementById('g-recaptcha-response').value = token;
            });
    });
</script>

Also I noticed that the reCAPTCHA tokens generated for the two domains have different lengths:

For a, the token is about 1100 characters.

For b, the token is around 2400 characters.

Can someone tell me what is wrong with this code?