Where to troubleshoot phpPgAdmin login issues?

I am getting "Login failed" errors when attempting to log into phpPgAdmin as user 'postgres'. In what file path would I find the relevant log files, to try and identify why the login is being rejected?

OS: CentOS 7
PostgreSQL: 9.6.6
pg_hba.conf settings for access:
# TYPE DATABASE USER ADDRESS METHOD

# "local" is for Unix domain socket connections only
local all all peer
# IPv4 local connections:
#host all all 127.0.0.1/32 ident
#host all all 127.0.0.1/32 md5
host all all 192.168.101.1/32 md5
# IPv6 local connections:
#host all all ::1/128 ident
host all all ::1/128 md5
# Allow replication connections from localhost, by a user with the
# replication privilege.
#local replication postgres peer
#host replication postgres 127.0.0.1/32 ident
#host replication postgres ::1/128 ident