Checks After Failover Setup
You can check if WAL data is streaming by running on the primary this command:
watch -d 'ps auxww|grep [s]treaming'
You will see something like this:
postgres 25972 0.2 0.1 103012 4912 ? Ss 15:24 0:09 postgres: wal sender process postgres 192.168.190.120(54248) streaming 26E/6A01AEF0
Where the last few hex digits will be changing if things are okay. (They will change fast on a busy system and possibly very slowly on a lightly-loaded one.)