How do I use my dedicated IP as the main shared IP for my clients in DirectAdmin?
In DirectAdmin, go to "IP Management" and click the checkbox next to the IP address you want to use for your accounts and then click the "Share" button.
That will enable the IP to be used as the default shared IP address for your reseller account.
If you want to assign that main shared IP address to any existing accounts, simply go to the users account and click the "Modify" tab.
After sharing the IP as mentioned above, in "Change the User's IP", you should now be able to choose your default shared IP address.