When you receive your certificates from Aust Secure there will be your site certificate (named yourdomain.crt) plus 2 others (GTECyberTrustRootCA.crt and ComodoClass3SecurityServicesCA.crt), these 2 must be installed as a certificate chain.

Sign onto the Webserver and select the server to manage.

Select the Security tab and then Install Certificate.

* Open the GTECyberTrustRootCA.crt in a text editor.

Select Server Certificate Chain, enter the password and copy the text from the GTECyberTrustRootCA.crt to the Message Text box (including the BEGIN and END lines),
then click OK.

Accept the certificate.

NOTE: Do not shutdown or restart the server until all steps have been completed.

Repeat the steps from * above using the text from the ComodoClass3SecurityServicesCA.crt.

For the site certificate again repeat the steps from * above, but this time choosing This Server instead of Server Certificate Chain.

At this stage all the certificates are installed and SSL now needs to be activated.

Select the Preferences tab and then Encryption On/Off.

Set encryption to 'On' and Port to 443, click OK, then Save and Apply.

Now shutdown and restart the server.