If you get Your connection is not secure error
You can get Your connection is not secure error in some browsers. That means that your website doesn't have SSL certificate yet.
SSL certificate is issued and renewed automatically when connecting your own domain to the Bitrix24 Site, but it may take some time to do that. As a rule, it takes from 30 minutes to 3 hours after connecting your domain and depends on the workload of the Let's Encrypt certificate authority. After the certificate is ready, it will be connected to your site, and this warning will not be appearing.
If you get This domain already exists error
Also, you can get this error message when you're trying to use the word bitrix in your own domain name. Just don't use this word and this error message will disappear.
If you get This domain already exists, but it was assigned to a site currently in the Recycle Bin error
When you delete the website, it's moved to the Recycle bin first. However, the domain name assigned to this website is not becoming vacant automatically. You need to restore the deleted website > change its domain name in the site settings and save changes. Now you can assign this domain name to a new website without getting this error.
Using CloudFlare DNS proxying
You need to disable DNS proxying in your CloudFlare account. Gray icon in the Status column with the DNS only sign means that DNS proxying is disabled. The orange one with the Proxied sign means that it's enabled.