Your reseller account comes with everything you need to get started, including 2 IP addresses, and the option between two excellent billing software packages, Clientexec and WHMCS (not included in the Bronze and Silver Reseller plans).
If you would like to purchase an additional IP address, you may do so through through your HostPapa dashboard:
Log in to your dashboard by visiting: https://www.hostpapa.com/dashboard
Click on My Services.
Click on Add Services.
Under Dedicated IP, click the Add to account button.
If you find you are running out of disk space or bandwidth for your clients, you may want to upgrade your reseller hosting plan. To do so, please submit a support ticket:
To open a support ticket, please log in to your HostPapa dashboard: https://www.hostpapa.com/dashboard
Support ticket tips/info: https://www.hostpapa.co.uk/knowledgebase/kb/how-to-open-and-access-support-tickets/