For latest cashier and stripe-php versions few thing need to be changed.
My cashier version is 7.0 ("laravel/cashier": "~7.0"
) and it automatically installs stripe-php 5. But some parameters has changed from stripe api. So this code will be working,
\Stripe\Stripe::setApiKey("sk_test_your_key");
\Stripe\Plan::create(array(
"amount" => 5000,
"interval" => "month",
"product" => array(
"name" => "Bronze standard"
),
"currency" => "eur",
"id" => "bronze-standard"
));
And you can read more in PHP section of stripe api docs...
(https://stripe.com/docs/api/php#create_plan)