Blesta

OpenPanel Enterprise edition has billing integrations with WHMCS, FOSSBilling and Blesta.

Blesta extension by BlestaClub​

OpenPanel Blesta extension allows users to integrate billing automations with their OpenPanel server.

Provided by BlestaClub:
https://blesta.club/extensions/openpanel

Open-source Blesta module​

An open-source Blesta module for OpenPanel is also available, maintained by the community.

GitHub repository:
https://github.com/Equitia/blesta-module-openpanel