From WHMCS Documentation
This command is used to delete a client from the database.
- clientid - ID Number of the client to delete
$postfields["action"] = "deleteclient"; $postfields["clientid"] = "1";
$command = "deleteclient"; $adminuser = "admin"; $values["clientid"] = 1; $results = localAPI($command,$values,$adminuser);
result=success clientid=xxx # ID of the deleted client
result=error&message=Client ID not found # Client ID is not given or found in the database.