ACF_To_REST_API::is_plugin_installed PHP Method

        public static function is_plugin_installed($plugin)
        {
            if (!function_exists('get_plugins')) {
                include_once ABSPATH . 'wp-admin/includes/plugin.php';
            }
            $paths = false;
            if ('rest-api' == $plugin) {
                $paths = array('rest-api/plugin.php');
            } elseif ('acf' == $plugin) {
                $paths = array('advanced-custom-fields-pro/acf.php', 'acf-pro/acf.php', 'advanced-custom-fields/acf.php');
            }
            if ($paths) {
                $plugins = get_plugins();
                if (is_array($plugins) && count($plugins) > 0) {
                    foreach ($paths as $path) {
                        if (isset($plugins[$path]) && !empty($plugins[$path])) {
                            return $path;
                        }
                    }
                }
            }
            return false;
        }

<?php

if (!defined('ABSPATH')) {
    exit;
}
$is_installed = ACF_To_REST_API::is_plugin_installed('acf');
$target = false;
$action = __('Install', 'acf-to-rest-api');
if (current_user_can('install_plugins')) {
    if ($is_installed) {
        $action = __('Active', 'acf-to-rest-api');
        $url = wp_nonce_url(self_admin_url('plugins.php?action=activate&plugin=' . $is_installed . '&plugin_status=active'), 'activate-plugin_' . $is_installed);
    } else {
        $url = wp_nonce_url(self_admin_url('update.php?action=install-plugin&plugin=advanced-custom-fields'), 'install-plugin_advanced-custom-fields');
    }
} else {
    $target = true;
    $url = 'http://wordpress.org/plugins/advanced-custom-fields/';
}
?>

<div class="notice error is-dismissible">
	<p><strong><?php 
esc_html_e('ACF to REST API', 'act-to-rest-api');
?>
</strong> <?php 
esc_html_e('depends on the last version of Advanced Custom Fields to work!', 'acf-to-rest-api');
?>
</p>
	<p><a href="<?php 
echo esc_url($url);