App: Application
WK: Wallkit
MC: Mailchimp
App → WK: Read configured interests with member/resource
WK → MC: Read configured category and interests
MC ⇢ WK: Provider catalog result
WK ⇢ App: items projection
App → WK: Subscribe selected member preferences
WK → MC: PUT subscribed member
MC ⇢ WK: Provider result
WK → MC: Read interest and merge labels
MC ⇢ WK: Label collections
WK ⇢ App: Extended provider fields plus user_id