Why is there no detailed error in Constant Contact sync report?

Due to a limitation in Constant Contact API that does not return detailed error SyncApps cannot report which email addresses have errors. Only error total is displayed like in the following text:

[Processed records=7, Updated=5, Error=2, Flagged as Opted-Out=0, Duplicated Email Address=0, Records With Blank Email Address=0, Previously Bounced=0, Filtered=0]

To see the detailed error you can open Constant Contact Activity Reports. Please click Contacts > Activity menu.

Usually, the errors are caused by contacts have been unsubscribed previously so cannot be updated by SyncApps.