I have followed every step to make sure UnwantedCommunicationReportingExtension will work with my app. Let me list here Adding a new target UnwantedCommunicationReportingExtension to my project Adding API endpoint to Info.plist <dict> <key>NSExtension</key> <dict> <key>NSExtensionAttributes</key> <dict> <key>ILClassificationExtensionNetworkReportDestination</key> <string>https://api.mycompany.net/call/v2/main/report</string> </dict> <key>NSExtensionMainStoryboard</key> <string>MainInterface</string> <key>NSExtensionPointIdentifier</key> <string>com.apple.identitylookup.classification-ui</string> </dict> </dict> </plist> Added classificationreport to Associate domain in Capability section. classificationreport:api.mycompany.net Created an apple-app-site-association file without json extension and returned this when api.mycompany.net called. I don't know whether to add app's bundle id or extension's bundle id. So added both. Complete apple-app-site-association below { "classificationreport": { "apps": [ "XXXXXX.com.company.appname.CallReport", "XXXXXX.com.company.appname" ] } } Checked the following website to ensure the file can be accessed. Both are displaying the file https://app-site-association.cdn-apple.com/a/v1/api.mycompany.net https://api.mycompany.net/.well-known/apple-app-site-association But I cannot call API https://api.mycompany.net/call/v2/main/report. It always fails with the following error Can anyone tell me what I'm missing? I tried for a week and was exhausted .