Builder domain is redirected to a different server (not to the builder server) and than you need to properly configure DNS record for the builder domain.
In order to migrate from Premium builder (license) to Enterprise license you need to take the following steps:
1. Un-install current builder plugin from hosting panel(s). You can notify your clients about temporary builder disabling before plugin un-installation. The whole process can take up to 1 day (we migrate data only on business days!).
2. Create Enterprise license in Site.pro account.
3. Setup builder domain and install builder using Builder installation guide link in Enterprise license.
4. Contact us in the ticket and inform us that you want to migrate to Enterprise license.
5. Wait for our response in the ticket when we collect and archive your clients' websites data in cloud builder server as well as transfer remaining days of Premium license validity to Enterprise license according to price difference between Premium and Enterprise plans.
6. In the ticket we will also specify URL of archived data containing your clients' websites. Download and extract data to your Enterprise builder installation with the following commands:
wget -O data.zip [URL-from-ticket]
php index.php /api/extract-websites?zip=data.zip
6. Install builder plugin on your hosting panel(s) using installation guide from Enterprise license.
If you face difficulties installing builder or extracting data let us know in the ticket and we will help you (we will need appropriate login details to your server).