I faced the same issue and resolved by enabling the funCaptcha in wordpress default registration page..
My Site: Aesthetic Today Spa Deals website
You can test the captcha in the following link, Aesthetic Today Partner Registation Link
Please let me know for any further fix regarding this..
I also tried the wp_nonce_url(), this doesn’t helped me..
For my website Aesthetic Today I copied the api key from FunCaptcha website and applied in FunCaptcha settings..
Hope this helps.. Thanks
