Hook not working on shop page / on sale page

I'm trying to target the after_main_content hook for my main shop page to add some content but if I target the page, it doesn't work at all.

The website is this one: http://www.saporidelbelice.com

I'm trying to do this mainly because I need to add SEO content bellow the main shop page
https://www.saporidelbelice.com/acquista-online/

while I also use this plugin: https://wordpress.org/plugins/on-sale-page-for-woocommerce/ to display a custom link on the main menu (the red one as of today) which seems to use the standard shop template with a custom product query.

If I add the content directly on the main shop page, it displays on top of the listing but this happens both in the main shop archive as well on the offer/sale page.

I'm trying to add the content bellow the results targeting the "on-sale" and "main-shop" pages using GP Hooks but they just don't work and Honestly I don't know what else to do.

Thanks in advance and have a good weekend :-)