Postgres SQL on AWS RDS how to grant permission for schema, select on tables to user I have logged in as superuser and created a readonly user.

When I run grant command, it says that schema does not exists

I am logging in as root:

sql -h myhost_name -U root -d postgres -W

grant usage on schema autorsid to readonly ;
ERROR:  schema "autorsid" does not exist


while schema does exists  but schema owner is not root.

Isn't when you are superuser, we should be able to grant permissions for all database/schema/tables etc.
Try grant with double quotes around schema name:

grant usage on schema "autorsid" to readonly ;