Mandatory Product Condition at checkout?

New Member
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Hi there,


I am having hard time trying to achieve what I am looking for.  I would like to check the cart and see if the user has selected a certain type of product or tag and if they have not selected a certain product with that tag I would like to force them to select one of the products that fall under that tag before they checkout. 

It is currently a legal issue that they are required to select both products before checkout. 

Please let me know,

THank you,