I spoke too soon. I tried to extend an other volume. Went through the steps and when I want to add replication task to the failover:
Error
iSCSI replication task not running
Failover configuration could not be saved because this iSCSI replication task is not running.
In order to resolve this issue please make sure this replication task runs on both local and remote node and it has correctly configured source and destination locations.
Task name: FunxTestSync:
Status: not running/disconnected