Class 'Braintree_Configuration' not found

So I'm trying to install Spark on Windows and Homestead.

I started on Windows, locally in cmd.

composer global require "laravel/installer"
cd code
laravel new myapp
cd myapp

Updated composer.json with

"repositories": [
    {
        "type": "composer",
        "url": "https://spark-satis.laravel.com"
    }
],

and added to require section in composer.json this

"laravel/spark": "~1.0",
"laravel/cashier": "~6.0"

then

composer update

Then added these in providers array in config/app.php

Laravel\Spark\Providers\SparkServiceProvider::class,
Laravel\Cashier\CashierServiceProvider::class,

then run

php artisan spark:install --force
php artisan spark:install --braintree --force

and then added this in onfig/app

App\Providers\SparkServiceProvider::class,

and finally

npm install
gulp

Then I switched to Homestead to do migrate

php artisan migrate

and I got this error:

[Symfony\Component\Debug\Exception\FatalThrowableError]
Class 'Braintree_Configuration' not found

Why is this happening? I mean, I installed spark with --braintree. How can I fix it?