Discounts at multiple item count

Hello everyone!
I’m researching everywhere in the plugins available for WooCommerce but after I tried a dozen discount-type plugins, none does what my client needs.

Lets say we have an online store for a physical shop. They sell badges, pins and clothings for college students. In the physical shop, they have a special discount for badges. When a customer buys 9 badges, the whole set have a 20% discount price. But if they buy a 10th badge, that one will have the regulr price. If the client buys 18 badges, then its a whole 20% discount – thats two sets of 9 they’re selling.

So we want the discount to be applied only at multiples of 9 items (all from the same category). So far, I only managed to achieve the global discount from 9 and up, and applying the discount to all products of that badge category in the cart.

One possibily without plugins is to create a special product called “badge kit”. This badge kit will have the set price and would allow the customer to choose any 9 items of the badge category, but I’m still to create this in a functional way – or leave it manual and make my client get the order and ask their client what are the 9 badges they want – a solution to avoid, since it would require even more store feedback to start to process each order.

Anyone knows a good plugin that allows any of these ideas?
– Either set a discount at multiples of 9 for a certain product category
– Or allow the customer to choose any 9 items from that category from within the “badge kit” product

Thanks!

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