Why am I getting permission denied on an ownership change?

My current user is pronto

mediapop_staging=> select current_user;
 current_user
--------------
 pronto
(1 row)

This user a standard super user created on AWS RDS.

mediapop_staging=> \du pronto
                        List of roles
 Role name |          Attributes           |    Member of
-----------+-------------------------------+-----------------
 pronto    | Create role, Create DB       +| {rds_superuser}
           | Password valid until infinity |

But I'm getting this:

mediapop_staging=> REASSIGN OWNED BY pronto TO mediapop_staging;
ERROR:  permission denied to reassign objects

Why? How can I resolve it?

Thanks to @Spike for comment, for solution which worked for me (source)

This assumes that objects are reassigned from role admin to role new_admin.

1.Create a new role:

mydb=> CREATE ROLE change_owner LOGIN;
CREATE ROLE

2.Make both the old owner and the new owner roles members of the newly created role:

mydb=> GRANT admin TO change_owner;
GRANT ROLE
mydb=> GRANT new_admin TO change_owner;
GRANT ROLE

3.Logout from psql and login using the new role:

$ psql -U change_owner mydb
mydb=>

4.Execute the reassignment:

mydb=> REASSIGN OWNED BY admin TO new_admin
REASSIGN OWNED

StackExchange Database Administrators Q#212279, answer score: 9