Unable to create SolusVM 2 VPS via WHMCS: Unprocessable Entity

Symptoms

1. Unable to create SolusVM 2 VPS via WHMCS:

   SVM_ERROR: [status code] 422 [reason phrase] Unprocessable Entity

2. The following error is seen in WHMCS > Utilities > Logs > Module Log with enabled debug:

   CONFIG_TEXT: {"message":"The given data was invalid.","errors":{"fqdns.0":["The fqdns.0 format is invalid."]}}

Cause

The hostname of VPS is not fully qualified domain name.

Resolution

Use fully qualified domain name for hostname of SolusVM 2 VPS in WHMCS - not example, but example.com.