ReCaptcha v2 suddenly cannot connect to server

-- HikaShop version -- : 2.5.0
-- Joomla version -- : 3.4.1
-- PHP version -- : 5.6.9
-- Browser(s) name and version -- : Chrome
-- Error-message(debug-mod must be tuned on) -- : We couldn't contact the reCaptcha server to verify your answer. Please try again.

Hi,
The HikaShop ReCaptcha v2 was working when it was set up. I have even gotten registration that lead to sales from users.

However, today it showed "We couldn't contact the reCaptcha server to verify your answer. Please try again." upon registering.

Please advise what can I do? I do not want to turn recaptcha off as we do get quite a lot of Spam registrations.

Thank you.

See the steps attached.