Recently I tried to setup some new physical standby databases and got the following strange message:
DGMGRL> ADD DATABASE "XXXX" as connect identifier is "XXXX" maintained as physical;
Error: ORA-16698: LOG_ARCHIVE_DEST_n parameter set for object to be added
Often you can read, that you have to check parameter log_archive_dest_2 on primary side. But this error message can also occur if log_archive_dest_2 on standby site points to another standby database.
Solution is following command on standby database to be added:
alter system set log_archive_dest_2 = '';