Many people face problems after switching WordPress website from current domain name to a new domain name. There are three reasons and solutions to solve this issue.
Nameservers of new domain is not correctly configured. If Nameservers are wrong it will not work while creating addon domain in cPanel. Please check the hosting provider with correct nameservers. Once nameservers are corrected the website will start working
Domain is still not propagating to new hosting servers. To solve this issue wait up to 24 hours for domain DNS propagation and contact domain administrator website afterwards.
Your current PUBLIC IP ADDRESS and LAN connection may be the problem. Even though you try multiple times you may be unable to access new domain WP dashboard. Simply turning off the modem after turning on again will solve the issue.
Sometimes cache and cookies of previous domain name in browsers will be reason for hindering access to new domain WP dashboard. Clearing all the cookies, cache and history from Google Chrome history will solve this problem.
Change Alternate DNS server settings to 188.8.131.52 in network connection of your computer
If all the above fails to work then there is a possibility in faulty WP database or some other issues during domain transfer. You should access hosting cPanel and login from Softaculous. You can also check wp database for any mistakes.
If all the above steps fail then you have wait 24 hours. It is because of DHCP DNS settings in regard with modem and computer and it takes 24 hours to automatically reset it. After 24 hours DNS servers cache expires. The next day you can access the website without any trouble. Changing the network provider can temporarily solve the issue.