OCI-16058
standby database instance not ready to receive redo log
Cause
The Remote File Server (RFS) process on the standby database was not ready to receive the redo log. To receive the redo log, the physical standby, snapshot standby, and far sync databases must be mounted to receive the redo log. There could also be a role change or some other activity on the target database that requested for non-receipt of the redo log during that operation.
Action
Check the standby alert log and RFS trace files for more information. Ensure that the database is mounted.