What am I missing?

Hey I was in amazon uk and I am selling a kit which has a retractable knife. It is allowed to be sold through FBA. However I got an email These items can only be sold to customers over 18 and must be shipped with an age-verified delivery method. We are requesting that you comply with the appropriate listing guidelines for age-restricted items by updating the customer_restriction_type attribute with the value “uk_18_knife

my listing has been removed . What should I do as The attribute is not there manually and through flat file.