Add custom text below Add To Cart button in WooCommerce single product pages

Solution:

You could try this (as you will see this is a CSS styling issue with theĀ margin-top):

add_action( 'woocommerce_after_add_to_cart_button', 'custom_content_after_addtocart_button', 100 );
function custom_content_after_addtocart_button() {
    // custom content.
    echo '<br/><div><p style="font-size:10px; font-style=italic; margin-top:20px;">(*Contact us for bulk purchase enquiry)</p></div>';
}

Code goes in function.php file of your active child theme (active theme or in any plugin file).

Tested and works. You will get that: