I received the following comments from the Examity service team.
" We suggest you follow the below steps and try again to make a payment.
PAYMENT ISSUE:
1. On your computer, open Chrome.
2. At the top right, click More. Settings.
3. Under "Privacy and security," click Site Settings.
4. Click Pop-ups and redirects.
5. At the top, turn the setting to Allowed.
Please follow the below steps to clear your browser cache and cookies data.
1. On your computer, open Chrome.
2. At the top right, click More.
3. Click More Tools to Clear browsing data.
4. At the top, choose a time range. To delete everything, select All Time.
5. Next to “Cookies and other site data” and “Cached images and files,” check the boxes.
6. Click Clear Data.
JAVA SCRIPT:
Please follow the below steps to activate JavaScript in your browser:
1. Open Chrome on your computer.
2. Click. Settings.
3. Click Security and Privacy.
4. Click Site Settings.
5. Click JavaScript.
6. Select Sites that can use Javascript.
Please restart your Chrome browser and try making the payment."
So to understand whether the system was the issue,I asked my wife to book an exam on my behalf from a different system and voila ! she was able to book one.