Do I Alter user quota in USERS tablespace?
Yes, users should not write to the system or sysaux tablespaces.  If the user is expected to have data or objects and will be copied to development instances they should have their own tablespace as it makes moving them easier.

Change your file path to what you have and execute this as a privileged user

create tablespace sales_tbs datafile '/home/oracle/databases/ora11/sales.dbf' 
 size 10M autoextend on maxsize 200M extent management 
 local uniform size 64K; 
alter user SALES quota 50m on sales_tbs;


and to make sure all future objects go to the dedicated tablespace for sales

 alter user sales default tablespace sales_tbs temporary tablespace temp;