pg_basebackup issue

Hello,

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