get_template_part() not working

I’m sure the function is working and I’m doing something wrong but…

In header.php of the parent theme, just after the opening <body> tag, I have

<?php get_template_part('partials/promo_bar', 'shipping') ?> 

In my child theme, I have a file located at partials/promo_bar-shipping.php who’s contents I was expecting to be displayed by that function however nothing is displayed.

What am I doing wrong?