Limiting the total amount of products in the cart

[FerminDiaz]

I am currently working on a beer selling shop, and one very specific requirement requirement is giving me issues:

The user can only checkout if the total amount of products in the cart is in a multiple of 6 (Example: If the user is buying 3 beers, it can't checkout, if the user is buying 6 beers, it can checkout, if the user is buying 7 beers it can't checkout, if it is buying 12, it can, etc..)

I assume something like that could be implemented by doing something like
if($cartamountvar%6!=0){
           *greys out checkout button*
}

But I'm having trouble finding the part of the code were I can add this

I am using prestashop 1.7.6.1

[Javi Leps]

Can you exchange your products for packages with 6 items?

[FerminDiaz]

A bit of an update but I found the module that does exactly what I needed

https://mypresta.eu/modules/ordering-process/cart-conditions-pro.html

I only had to have every product in the same category (beer category in this case) and limit the category to the 6 limit