Hi Satish,
I checked your trouble, because you created design schema by .hdbschema, so you can not exec grant sql command, if you want to grant schema to relevant user, you can use below sql command.
call "_SYS_REPO"."GRANT_SCHEMA_PRIVILEGE_ON_ACTIVATED_CONTENT"('SELECT','MYSCHEMA','<user name>');
Hope this can help you.
Regards,
Jerry