validate trade agreement for sales line item

Hi,

In D365 for operations, I want to validate each sales Line against the valid trade agreement for items.

A valid Trade agreement exists for item.

Also there is a trade agreement available for the item configuration i.e. Size. but this is expired one and hence invalid.

Now I want system to throw validation message if user select the Size and it should not save that salesline.

Please let me know what should be right place to put such validation business logic as I am not aware where Standard AX system validates trade agreement for the item in Sales LIne.

Any hint would be much appreciated.