Enable mod proxy on the server
Mod proxy is required for routing traffic to your Proxy
# enable apache module for proxy
sudo a2enmod proxy
sudo a2enmod proxy_http
# restart apache
Modify sites-available config file
Below is an example of configuring the customer's server to route all traffic to customerdomain.com/campaign/ to the Proxy you created for the customer.
# continue VirtualHost entries..
# at beginning of Directory rules
RequestHeader set Host customerdomain.com
Allow from all
# continue normal configuration..