Test connection to Plesk from WHMCS fails: Unable to find appropriate manager for this version of Panel in WHMCS

Symptoms

Test connection to Plesk from WHMCS fails:

PLESK_INFO: FAILED: Error code: 0. Error message: Unable to find appropriate manager for this version of Panel. Plesk should be at least 8.0 version

Cause

Possible reasons:

1. WHMCS uses HTTP connection instead of HTTPS to connect to Plesk API.

2. The option Ability to use remote API is disabled for a reseller in Plesk.

3. The server where WHMCS is installed is not authorized to run WHMCS.

4. The Plesk server hostname resolves to two IP addresses and one of these IP addresses does not exist on the network interface of this Plesk server.

   Example: The Plesk hostname server.example.com resolves to two IP addresses:

   # nslookup server.example.com
   
   Name:    server.example.com
   Address: 203.0.113.2
   Name:    server.example.com
   Address: 203.0.113.5

   But the IP address 203.0.113.5 does not exist on the Plesk server.

Resolution

Make sure that the following requirements are met:

1. The option Tick to use SSL Mode for Connections is checked in WHMCS.

   
   
   
   

2. When reseller credentials are used to establish a connection, the option Ability to use remote API has to be enabled for this reseller in Plesk at Resellers > John Doe > Customize (Under Resources) > Permissions tab.

3. The hostname is authorized to run WHMCS. To check this, use the WHMCS License Verification tool.

4. Make sure that the Plesk hostname is resolved to a valid IP address that exists on the Plesk server. In case there is an extra IP address that does not exist on the Plesk server, but points to the Plesk hostname, remove it on registrar's side or add it to Plesk.