Site breaking when I call a custom module up on app.php file

My Craft CMS version 3 site is breaking when I boostrap a custom module up on app.php file.

The code looks like this:

<?php

use craft\helpers\App;

return [
    'id' => App::env('APP_ID') ?: 'CraftCMS',
    'modules' => [
        'my-module' => \modules\Module::class,
        'fa-forms' => \faforms\Module::class
    ],
    'aliases' => [
        '@subdomain' => 'http://subdomain.localhost',
    ], 
    //'bootstrap' => ['fa-forms'],
    //'bootstrap' => ['my-module'],
    'components' => [
        'queue' => [
            'ttr' => 3600,
        ],
    ],
];

If I uncomment the bootstrap for the fa-forms module I get a server error that I cannot trace because it prevents the debug toolbar from loading.

Has anyone had a similar issue with bootstrap breaking their site?