Customize email heading in customer_invoice.php

How do I change the text in the email heading of customer_invoice.php – Now it says “Faktura för beställning #18514” and I just want to change it to “Kvitto för beställning #18514” I have tried the code below with no luck

Many thanks in advance!

/Jonas

function filter_woocommerce_email_heading_customer_invoice( $email_heading , $email ) {
// make filter magic happen here...
$email_heading = 'Kvitto för beställning';
return $email_heading;
};

// add the filter
add_filter( "woocommerce_email_heading_customer_invoice", 'filter_woocommerce_email_heading_customer_invoice', 10, 2 );