Using WHMCS module for CyberPanel, you can sell or automate basic functions of CyberPanel for your customers. You can install this module by following WHMCS server module installation steps. Here they are again:-
git clone https://github.com/jetchirag/cyberpanel-whmcs.git cyberpanel
Data supplied is not accepted, following characters are not allowed in the input ` $ & ( ) [ ] { } ; : ‘ < >.
Solution: Remove those special character from service's password
API Access Disabled.
Solution: Enable API Access from CyberPanel for user
Unknown Error Occurred
Solution: Usually means WHMCS is unable to reach api. Ensure hostname/ipaddress is correct and CyberPanel access port is open i.e. 8090 in firewall.