Cas91

You can use this new CSS code
/* Show category nav links */ div.nested-category-tree-wrapper { display: flex !important; float: none !important; min-width: 100% !important; max-width: 100% !important; margin-right: 0 !important; } section.products.collection-content-wrapper.products-list { flex-direction: column !important; display: flex; } .nested-category-tree-wrapper>ul { width: 100% !important; display: flex; justify-content: center; align-items: center; flex-wrap: wrap !important; padding-bottom: 15px !important; padding-top: 15px !important; border-top: 1px solid; border-bottom: 1px solid; margin-bottom: 20px; background-color: #e1d5c9; } .nested-category-tree-wrapper>ul li { margin-left: 2vw; } nav.nested-category-breadcrumb { display: none !important; } ul.nested-category-children { display: none !important; } a.category-link.root { padding-top: 17px !important; } div.nested-category-tree-wrapper a.category-link { padding-top: 0px !important; padding-bottom: 0px !important; }  

Also very much wish this was a thing as discount codes simply don't cut it for many applications.
Commenting in hopes this will be introduced by SS soon.

Hi. This happens because, when you are clicking the link, you are already logged in with your 'Site 1' login details. As you are already logged in with your 'Site 2' ID, it won't let you use another.
The trick is to right-click the contributor invitation link that arrives by email and choose to open it in a Private or Incognito window. You should then be able to accept the invitation.
These permissions aren't affecting the issue with invitations, but the template author should not remain as the owner of the site. Shortly after purchase, I would expect the template author to transfer ownership of the site to you. If this hasn't happened within a reasonable period of time then I recommend that you contact them and ask them to do so. Only the current site owner can transfer ownership of the site. 
After they transfer ownership to you, the former owner may remain as a contributor with administrator permissions, unless they manually remove themselves. If you don't want them to have permissions on your site, you can remove the previous owner.
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Thank you Paul, really appreciate your help.
Thanks for the tips about redemption as well, I will definitely factor those in. 

I am not aware of any published limits for the number of discount codes you can have, so it may be worth checking with Squarespace Customer Care in case there's an unpublished limit. Let us know what they say 🙂.
Note that are some differences between gift cards and discount codes:
Gift cards can be used multiple times until the value is depleted.  Gift cards can apply to shipping. Discounts don't' apply to shipping as they are applied to the subtotal. Did this help? Please give feedback by clicking an icon below  ⬇️