Add in a custom prefix and suffix to WooCommerce Order Number

functions.php

add_filter( 'woocommerce_order_number', 'change_woocommerce_order_number', 1, 2);

function change_woocommerce_order_number( $order_id, $order ) {
    $prefix = '#SAM-';
    $suffix = '-' . date(Y); 
    return $prefix . $order->id . $suffix;
}

https://stackoverflow.com/questions/38783349/adding-suffix-and-prefix-to-woocommerce-order-number-without-using-a-plugin