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) {
    $response = localAPI('GetEmailTemplates');
    $emailTemplates = array('none');
    foreach ($response['emailtemplates']['emailtemplate'] as $emailTemplate) {
        array_push($emailTemplates, $emailTemplate['name']);
    }

    $configOptions = array("Create_Mail" => [
        "FriendlyName" => "Create Action E-Mail Template",
        "Type" => "dropdown", # Dropdown Choice of Options
        "Options" => $emailTemplates,
        "Description" => "E-Mail Template auswählen",
        "Default" => "option1",
    ]);

    logModuleCall(
        'iServiceAddon',
        __FUNCTION__,
        $configOptions,
        'Debug',
        $emailTemplates
    );

/*    return array(
        'Dropdown Field' => array(
            'Type' => 'dropdown',
            'Options' => array(
                'Display Value 1',
                'Second Option',
                'Another Option',
            ),
            'Description' => 'Choose one',
        )
    ); */
    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',
        ),
    );
}