Create a Shopify cart rule

[AASampaio]

How can I create a Shopify cart rule where I can't mix product categories?
Example: the customer will not be able to have surfboards and t-shirts in his cart, or has a surfboard or has a tshirt, because the shipping cost is different in both categories.

[sniper2804]

Why don't you just add up the shipping prices for both the types of product when they are in cart, instead of blocking the customers on checkout?

[AASampaio]

Because the processing of surfboards is different from t-shirts, for example: different carriers etc...