OrderItem get_total() returns lower value than $order_item->get_product()->get_price() * quantity

The problem seems to be related to missing tax or (and) to applied coupon discount.

The WC_Order_Item_Product method get_total() is the discounted line item total without taxes. In this case when a coupon is used, the discount is applied to the item depending of the coupon type and restrictions.

The WC_Order_Item_Product method get_subtotal() is the non discounted line item total without taxes.

When there is no discount (no coupon applied), get_total() and get_subtotal() have the same value.

So in your case, you may need to add the taxes using one of this WC_Order_Item_Product methods:

• get_total_tax() method as discounted line item tax total
• get_subtotal_tax() method as non discounted line item tax total

and to sum them with the corresponding total to get the line item total with tax like:

foreach( $order->get_items() as $item ) {
    $item_total = $item->get_total() + $item->get_total_tax(); // Discounted total with tax
}

or

foreach( $order->get_items() as $item ) {
    $item_total = $item->get_subtotal() + $item->get_subtotal_tax(); // NON discounted total with tax
}

So this time you will get the correct amount.

---

Related: Get Order items and WC_Order_Item_Product in WooCommerce 3