There is a mistake in your IF statement condition where =
has to be replaced with ==
or ===
. Also with coupons, you need to use the coupon code slug (but not the post ID).
To display a message on Order received page better use woocommerce_thankyou_order_received_text
filter hook, this way (for Woocommerce 3+):
// On "Order received" page (add a message)
add_filter( 'woocommerce_thankyou_order_received_text', 'thankyou_applied_coupon_message', 10, 2 );
function thankyou_applied_coupon_message( $text, $order ) {
$coupon_code = '1635'; // coupon code name
foreach( $order->get_items('coupon') as $coupon ){
if( $coupon->get_code() === $coupon_code ){
$text .= '<p>'.__("This is an custom thank you.").'</p>';
}
}
return $text;
}
Code goes in function.php file of your active child theme (or active theme). It should works now.
Updated
For the versions of Woocommerce before 3.0, you should use use the following instead:
// On "Order received" page (add a message)
add_action( 'woocommerce_thankyou', 'thankyou_applied_coupon_message', 10, 1 );
function thankyou_applied_coupon_message( $order_id ) {
$coupon_code = '1635'; // coupon code name
$order = wc_get_order( $order_id );
foreach( $order->get_items('coupon') as $coupon ){
if( $coupon['name'] === $coupon_code ){
echo '<p>'.__("This is an custom thank you.").'</p>';
}
}
}
Code goes in function.php file of your active child theme (or active theme). Tested and works.