Cannot contact reCAPTCHA. Check your connection and try again

Solution 1:

While registering reCaptcha, I gave Domain as localhost. It solved the error for me. (I am using Visual Studio 2017, and I am running my web application on localhost.)

Solution 2:

Define domain name like this, While working with localhost

Solution 3:

I had the same problem (continuous messages "Cannot contact reCAPTCHA. Check your connection and try again") which drove me crazy.
Then I discovered that I had registered a "reCaptcha V2" for my site, but used the site key and the secret key to create an "invisible reCaptcha".
After registering an "invisible reCaptcha" for the same domain, I got a different key pair that worked flawlessly.
I concluded that the three types of reCaptcha (V2, invisible and Android) produce specific key pairs. Every key pair is unique for the reCaptcha type that has been registered for the domain, and cannot be used interchangeably for other reCaptcha types. On the other hand, one may register different reCaptcha types for the same domain, if needed.