storefront_is_product_archive. So you are calling it twice and that causes issues. On line 22 of file /home1/lharkins/mu-tang.com/wp-content/themes/storefront-child/inc/storefront-functions.php of your child theme you added it. In the parent theme it is on line 31 of file /home1/lharkins/mu-tang.com/wp-content/themes/storefront/inc/storefront-functions.php it is already in use. So no need to do things twice..
As you are new to this all I suggest you use this boilerplate Storefront child theme and focus on needed CSS changes only.
If you do need code changes only add functionality for that, don’t clone the parent. The latter can cause errors like you are experiencing. Use the boilerplate mentioned and added functionality as needed.
NB Do also check official documentation on Child themes
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