The website WITH / WITHOUT a ‘www’ before domain name does not open

The website WITHOUT a ‘www’ before domain name does not open

Most likely, you have not added the domain itself but a subdomain thereof (www.your-site.com) while adding the domain via the hosting control panel. Such adding operations are not correct. You need to create the domain via the hosting control panel once again. This time, don’t put a ‘www’ in the beginning of the domain name:
How to add a domain to the hosting.

The website WITH a ‘www’ before domain name does not open

Check if there is a resource A-record or CNAME-record with a ‘www’ in the nameserver settings. If it’s not there, add a new one and wait for nameservers to update (this may take about 24 hours).

To add a CNAME record for ‘www’ subdomain, follow the instructions:
How to add a CNAME record.