When you deploy Magento to live server, everything is working fine, except when you save the configuration in back-end the issues occur.

If it shows this message “Magento Fatal error: Class ‘Net_IDNA2’ not found in…..” you should not worry about it, because it is not your Magento’s issue, it is the server issue.

When you installed server, you did not install full php extensions, so it will lack some of them.

In this case you only need to install

php-intl

You can do it by the following command

sudo yum install php-intl

Hope it will help you solve the issues.