How to add trust badges right below Woocommerce place order button

I tried this code and for some strange reason I keep getting an error in my fucntions.php Therefore the code won’t save properly. It keeps getting rolled back.

add_action( 'woocommerce_review_order_after_payment', 'add_content_on_checkout' );

public function add_content_on_checkout() {
      echo "<img src='safe_checkout.png' >"; //add the image url in the src attribute
}

I have already successfully added badges below my proceed to check out button on the cart totals page.

The website where I copied the code is here and this is the look I’m trying to achieve. Is there an optional way to do this using custom CSS?

The page I need help with: [log in to see the link]