Let's start with couple of words on captcha's algorhytm, let's see what traffic and at which point is being sent.
1. User enters the page and the recaptcha form is uploaded from google
2. User clicks the checkbox and solves the captcha
3. When the captcha is solved, google checks the answer and returns code to the user in the field <textarea id="g-recaptcha-response"
4. User fills all
This was working for me quite well before. I'm referencing a single site that has multiple pages. It looks like one page worked last night but in many cases, I am constantly getting the Sorry I Cannot Solve Your Given Captcha error despite providing the correct domain key. And to make it worse, each time I get the error, I'm still charged credits.