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The browser address bar will show “Not Secure” because you don’t have a valid SSL certificate. To fix this, simply install one by following this:
Then wait for up to 30 minutes and try visiting your site using https:// instead of http://.
If you want everyone to stop seeing the “Not Secure” warning, just force HTTPS:
As for the Bitdefender warning, check if installing an SSL certificate resolves it. If it doesn’t, your domain was likely listed on their blocklist (a false positive). In that case, you’ll need to contact them directly to get your site removed from the blocklist, since we can’t do anything about it on our end.