Sloth hi, are you getting any errors in your browser's developer console?
To help you troubleshoot further if you aren't getting any errors, can you please post the output of php flarum info
ran from the root of your Flarum installation?
Please also check your Flarum error logs to see if you find anything there pertaining to your issue as well 🙂
Edit: Additionally, did you copy your site and secret key from reCAPTCHA admin panel and add them to your extension settings?