The most common cause of an additional IP address failing to operate properly is that the IP address is marked as “disabled” in your myCP control panel. To enable your additional IP address(es) please visit your myCP control panel and click the link to “Enable / Disable IPs” in the left-hand column.
Please note that all additional IP addresses are delivered to our customers in the “disabled” state so you will need to specifically enable the IP addresses before utilization.
There are many other factors which may contribute to the failure of an additional IP address. Most of these relate to how your server handles issues such as routing with multiple IP addresses, especially if they reside in different subnets. As each of these cases are quite unique please open a Support Ticket if you are still unable to utilize your additional IP addresses.