What do you mean you bought a license? DirectAdmin has NO resellers and other companies may either supply it with a machine they sell or with a machine they rent out, but no one except DA can sell it to you as a product.
Are you installing DirectAdmin yourself?
Are you installing it on the same server it was purchased for?
If you got the license from leaseweb then they're responsible for the installation.
You can probably get a lot of questions answered here; and because Debian is still in beta test you may be able to get a response from the DA support team. I'd try asking them.
Check the DirectAdmin website and click on "Support" for information.
Iv tried to get Leaseweb to do it for me but they want $$
Whys the live support always off
Iv emailed for support but iv had no reply is everyone on hoilday LOL
It's appears that your server doesn't have the minimum software on it that it needs to support a DirectAdmin install.
If you cannot get through these issues as they come up you may have to pay someone to do the install for you or switch to a vendor who can supply a properly supported DA server for you.