ORA-16700: The standby database has diverged from the primary database.
https://subhanuddinkhadri.blogspot.com/2015/10/flashback-standby-after-resetlogs-on.html
http://anuj-singh.blogspot.com/2018/06/oracle-flashback-for-standby-database.html
Error code: ORA-16700
Description: the standby database has diverged from the primary database
Cause: The primary database may have been flashed back or restored from a backup set and then reopened with the RESETLOGS option.
Action: Re-create the standby database from the primary database or flash back the standby database to the same point the primary database had been flashed back to.
How to deal with ORA-16700:
We do not have to rebuild our standby, just move standby database using flashback to a previous SCN value when the incarnation of primary and standby was same. Start the MRP manually or bounce the configuration in DG broker.