I thought the billing manager is free. Why do you want $25?
HostGator provides the license to use WHMCS for free; however, the installation and configuration of the software require administrator assistance, for which HostGator charges for some third-party software. You may install and configure this software yourself, and it will only be invoiced if you request to have us install it on your behalf.
We will provide the software via Softaculous and installation instructions to you. If you want us to install the software, you may contact us via phone or Live Chat requesting that we install this for you, including the license key you received and authorizing the $25 charge.