First make sure that API access is enabled by going to OpenAdmin > API or by running opencli config get api from the terminal.

WHMCS server needs to be able to connect to OpenAdmin on port 2087, whitelist both servers: csf -a SERVER_IP.

SSH to your WHMCS server and inside path_to_whmcs/modules/servers run this command to download the module: git clone https://github.com/stefanpejcic/openpanel-whmcs-module.git openpanel.

From WHMCS System Settings > Products & Services > Servers click on Create New Server and under module select openpanel then add server IP, username and password for the OpenAdmin.

Create a new group, then create new plans under this group. When creating products, make sure to select openpanel for Module and the newly created group