Confirm there are not already settings or features that do what the shop is asking for.

When setting up a mystery item, we are unable to restrict or apply the offer to a specific collection because that collection is set to "hidden" within the app/store setup. Because hidden collections do not appear in the "Limit to Collections" dropdown menu, we cannot link the mystery item to the intended products.

What does the shop want the product to do? Include all collections—both visible and hidden—in the "Limit to Collections" dropdown, or add a toggle option within the dropdown setting to "Show hidden collections."

Why/how would it improve sales or efficiency? Shops frequently use hidden collections specifically for mystery items, custom bundles, or exclusive VIP promotions to keep them isolated from standard storefront browsing.