There has been a critical error on this website.

Editing the site URL does not automatically make the site accessible at the new URL. You need to update all the URLs in the WordPress database too.

Now, change the site URL back to https://tssb.talentsynergy.com.my you can do it by editing wp-config.php https://developer.www.ads-software.com/advanced-administration/upgrade/migrating/

After you revert the change, install new WordPress on https://talentsynergy.com.my and then migrate https://tssb.talentsynergy.com.my to https://talentsynergy.com.my (use a WP migration plugin)

Please look at this article for how to enable and log errors so that you can see what the actual error is:
https://developer.www.ads-software.com/advanced-administration/debug/debug-wordpress/

Problem solved. Thank you for your support, Mr. Liew Cheon Fong and Ms. Jamie.