A base is needed to be restored on the destination server, so we can start a clean point from which we can continue the replication. This process is also called: INITIAL LOAD:

We will use a full backup with duplication for standby:

RMAN> backup database include current controlfile for standby plus archivelog;

starting full resync of recovery catalog
full resync complete

Starting backup at 16-JAN-18
current log archived
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=197 device type=DISK
channel ORA_DISK_1: starting archived log backup set
channel ORA_DISK_1: specifying archived log(s) in backup set
input archived log thread=1 sequence=2598 RECID=2536 STAMP=965354598
input archived log thread=1 sequence=2599 RECID=2537 STAMP=965358183
input archived log thread=1 sequence=2600 RECID=2538 STAMP=965361802

********************************************************************

Once the backup is done transport the backups to the destination(replica) server:

Important INFO: We should be SURE about the SCN, AFTER WHICH we want to SYNC. So in order to do that, we need to extract the media recovery ENDING SCN as follows:

RMAN> restore database preview summary;

Starting restore at 16-JAN-18
using channel ORA_DISK_1


List of Backups
===============
Key     TY LV S Device Type Completion Time #Pieces #Copies Compressed Tag
------- -- -- - ----------- --------------- ------- ------- ---------- ---
210342  B  F  A DISK        16-JAN-18       1       1       NO         TAG20180116T124843

List of Archived Log Copies for database with db_unique_name DBNAMEL
=====================================================================

Key     Thrd Seq     S Low Time 
------- ---- ------- - ---------
210341  1    2665    A 16-JAN-18
        Name: +BANKINGFRA/DBNAMEL/ARCHIVELOG/2018_01_16/thread_1_seq_2665.294.965566171

recovery will be done up to SCN 474514374
Media recovery start SCN is 474514374
Recovery must be done beyond SCN 474514374 <------ THIS ONE
to clear datafile fuzziness
Finished restore at 16-JAN-18

RMAN>  

This means, that our duplicated database,WILL be consistent UP TO: 474514374. Any changes done after that on the sourceSRV, WILL NOT be visible in the duplicated database.

Copy the backup files to the replica server:

sourceSRV$ scp ora_df* root@destinationSRV:/home/oracle