whmcsServiceAddon/serviceAddon.php

<?php

if (!defined("WHMCS")) {
    die("This file cannot be accessed directly");
}

function serviceAddon_CreateAccount(array $params) {
    logModuleCall(
        'iServiceAddon',
        __FUNCTION__,
        $params,
        'Debug',
        App::self()
    );
    return 'success';
}

function serviceAddon_SuspendAccount(array $params) {
    return 'success';
}

function serviceAddon_UnsuspendAccount(array $params) {
    return 'success';
}

function serviceAddon_TerminateAccount(array $params) {
    return 'success';
}

function serviceAddon_ChangePackage(array $params) {
    return 'success';
}

function serviceAddon_TestConnection(array $params) {
    return 'success';
}

function serviceAddon_UsageUpdate(array $params) {
    return 'success';
}

function serviceAddon_ConfigOptions(array $params) {
    $configOptions = array();
    return $configOptions;
}

function serviceAddon_MetaData() {
}

function serviceAddon_AdminCustomButtonArray($params) {
}

function serviceAddon_AdminServicesTabFields($params) {
}

function serviceAddon_ClientArea($params) {
    return array(
        'tabOverviewReplacementTemplate' => 'templates/clientarea',
        'vars' => array(
            'test1' => 'hello',
            'test2' => 'world',
        ),
    );
}