Hello, first thanks for your purchase.
I did a test and saw that’s returning an empty request in the ajax process of contact form:

Normally this is caused when value of variable $debug is different from 0. You mentioned that already tried with 0, can you double check it ?
The variable should be like below:
$debug = 0;
If even so the problem still persists, please share with us all code of your php/contact-form-recaptcha-v3.php. You can use a service like https://pastebin.com to generate a link with the code and share with us.
Please try that and let us know if you need further assistance.
Kind Regards,
Rodrigo.
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