Oracle Message ORA-16802 - downgrading redo transport mode from SYNC disallowed

ERRORdowngrading redo transport mode from SYNC disallowed
CAUSEAn attempt was made to downgrade the redo transport mode of a standby database from SYNC to ASYNC when the configuration was in Maximum Protection or Maximum Availability mode and the primary database was a RAC database. This was not disallowed even though there may have been other standby databases with redo transport modes set to SYNC to support the protection mode.
ACTIONDo one of the following if the redo transport mode of the standby must be downgraded: - Shut down all instances of the primary database and restart one instance with the initialization parameter CLUSTER_DATABASE set to FALSE. Downgrade the redo transport mode of the standby database of interest. Then, shutdown the instance, set the the CLUSTER_DATABASE initialization parameter to TRUE, and restart all primary database instances. - Downgrade the protection mode to Maximum Performance mode and then, downgrade the redo transport mode of the standby database of interest. Finally, upgrade the protection mode. This will require a restart of all primary database instances if upgrading to Maximum Protection mode. Note that the above only works when there is at least one standby database in the configuration that has its redo transport mode set to SYNC.