upgrade to PG11 on secondary fails (no initdb was launched)

Hey,

I have 2 nodes that are configured with streaming replication (PG 9.6, repmgr 4.3).

I was trying to upgrade the nodes to PG11 with the doc - https://www.postgresql.org/docs/11/pgupgrade.html

Everything goes well until I try to start the secondary and then it fails on the next error : 

2019-05-23 04:17:02 EDT  23593  FATAL:  database files are incompatible with server
2019-05-23 04:17:02 EDT  23593  DETAIL:  The database cluster was initialized with PG_CONTROL_VERSION 960, but the server was compiled with PG_CONTROL_VERSION 1100.
2019-05-23 04:17:02 EDT  23593  HINT:  It looks like you need to initdb.
2019-05-23 04:17:02 EDT  23593  LOG:  database system is shut down

I upgraded the primary, then I run the rsync command in the primary : 

rsync --archive --delete --hard-links --size-only --no-inc-recursive /var/lib/pgsql/data /var/lib/pgsql/11/data/ secondary_ip:/var/lib/pgsql/data/

in the secondary I checked the version file and it was 11 : 

[secondary]# cat PG_VERSION
11

Any idea how to handle it ?