Is there is a way to enter zero dollars price value (e.g. for a loyalty card) in the National Product Catalogue?
It depends who the retailer is.
Woolworths and Progressive allow a zero price only for Allowances and Charges. You cannot enter a $0 List Price or Transaction Price for Progressive.
For Foodstuffs, the Price Value may be zero by setting the Ref Doc ID to 'EXCEPTION’.