The app verifies the phantom server by making 2 REST calls to the phantom server - /rest/cef - /rest/cef_metadata This error is indicating that there's a problem with the CEF field definitions, specifically the CEF fields configured in Phantom.   You can check the entire list via https://<phantom>/rest/cef/ & https://<phantom>/rest/cef_metadata. Look for something like a null field or a list within a list (not allowed).  If you identify the problematic field, go to Admin > Admin Settings > CEF and remove the field in question and re-try the connection from the App. List within a list Example (Bad): "Example": { "contains": [ ["*"] ] }, ... View more