Method 1: Check the postman cache and try in new tab.
Method 2: type CTRL+R enter cmd then type ping domainname.com (without http and www) and enter, check if any response is coming.
Method 3: type CTRL+R enter cmd then type
Method 4: type CTRL+R enter drivers then goto this path(C:\Windows\System32\drivers\etc\hosts) and enter edit the host file & add and save it. below line with IP. ie. destination server domain or IP details.
after that try in postman or browser it will work accordingly.
Example.
100.00.00.100 domain.name.com