Adding Stripe invoice API param

<?php

/*
 * Not yet fully tested
 */
function my_em_stripe_payment($stripe_checkout,$EM_Booking){
 $stripe_checkout['payment_method_types'] = ['card', 'sepa_debit','sofort','us_bank_account'];

 $stripe_checkout['invoice_creation'] = [
										'enabled' => true,
										'invoice_data' => [
															'footer' => 'Thank you for your business!',
															'metadata' => [
																'booking_id' => $EM_Booking->booking_id,
															],
														]
										];

 $stripe_checkout['customer_email'] = $EM_Booking->get_event()->get_contact()->user_email;

 return $stripe_checkout;
}
add_filter('em_gateway_stripe_checkout_session_vars', 'my_em_stripe_payment', 100,2);