Ocado, what does only 18 promotions mean

[RedRiverShore6]

Does this mean that you can only buy 18 promotional items across the shop which doesn't seem very many or only 18 of each item which seems fine, it's not very clear and I don't want to have more than 18 promotional items across my shop and be charged more for the extra ones. Everything that has any offer on it seems to have this message.

Isn’t it 18 of each item to prevent people hoarding offers to sell on?
So you could buy up to 18 bottles of wine, 18 yogurts, 18 packets of biscuits in one shop?

Thanks, I was hoping it was that and not across the shop.