General Public & Transcend

I'm a little confused by this part of the transcend and tessitura document

Postal codes are required for each Direct Marketing and Ecommerce transaction. The implication of this is that if you accept credit cards against a general public constituent, that constituent will need to have an address assigned to it that contains a postal code (for example, the location of your venue). Otherwise, Direct Marketing (card-keyed) transactions will be rejected by TranScend.

How do I make sure our general public constituent has an address attached?

Thanks!