Grant other users access to invoices

Unfortunately, the suggested work-around to provide other users with access to view invoices isn’t working. I attempted to insert the code provided for this in the FAQ, into my functions.php file, and there was no difference in permissions. I also found another thread here where the same code was suggested, and the person doing the inquiring had found a workaround to add the user roles directly into the plugin’s file woocommerce-pdf-invoices.php. However, that does not work also.

I am attempting to reveal the invoice to users logged in to a custom role, Cashier.

I cannot find permissions for this plugin in the WP plugin User Role Editor, either.

Please help. How can my cashiers have access to these invoices for printing purposes, other than to email everyone a copy of the invoices? They need to be able to download it from the WP admin and not have to be given loads of extra permissions like Shop Manager, Administrator etc.