pg_basebackup issue

Hi Team,

I am using Postgresql 9.5 and I have created backup_admin user and created
dba_admin ROLE with SUPERUSER and REPLICATION ,after that GRANT dba_admin
role to backup_admin user and executed pg_basebakup utility with
backup_admin user.
But I am not able to use the pg_basebackup utility using backup_admin user
and got below FATAL.
pg_basebackup: could not connect to server: FATAL: must be superuser or
replication role to start walsender

However I have observed only issue with backup_admin user to use
pg_basebackup utility.

Please help me to understand why pg_basebackup is throwing FATAL when I use
backup_admin?.

Is there any limitation with pg_basebackup utility ?

The process i am following for backup_admin user :

postgres=# select version();
version
----------------------------------------------------------------------------------------------------------
PostgreSQL 9.5.5 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.1.2
20080704 (Red Hat 4.1.2-55), 64-bit
(1 row)

postgres=#
postgres=# create user backup_admin password 'XXXXX';
CREATE ROLE
postgres=# create role dba_admin SUPERUSER REPLICATION;
CREATE ROLE
postgres=# grant dba_admin to backup_admin;
GRANT ROLE
postgres=# alter user backup_admin set role to dba_admin;
ALTER ROLE

postgres=# \du
List of roles
Role name | Attributes
| Member of
------------------+------------------------------------------------------------+--------------------
backup_admin |
| {dba_admin}
dba_admin | Superuser, Cannot login, Replication
| {}
postgres | Superuser, Create role, Create DB, Replication, Bypass
RLS | {}

[postgres(at)pgserver ~]$ mkdir online_backups1
[postgres(at)pgserver ~]$ /opt/PostgreSQL/9.5/bin/pg_basebackup --format=t
--pgdata=online_backups1 -p 5432 -U backup_admin -x -z --verbose
pg_basebackup: could not connect to server: FATAL: must be superuser or
replication role to start walsender

*Please help me why pg_basebackup is throwing FATAL when I use
backup_admin?.*

*Is there any limitation in pg_basebackup utility ?*

For information the pg_basebackup is working fine for Postgres user and it
is successful.

[postgres(at)pgserver ~]$ /opt/PostgreSQL/9.5/bin/pg_basebackup --format=t
--pgdata=online_backups -p 5432 -U postgres -x -z --verbose
transaction log start point: 0/2000028 on timeline 1
transaction log end point: 0/2000130
pg_basebackup: base backup completed

Thanks,
Chiru