"Table or view does not exist" on synonym I have a database and a USER administrating it. Then I have an additional USER_APP to whom I granted CRUD access to all tables in my oracle data modeler (and then applied these via generated script )

I created a synonym for every table from USER_APP account, with the following syntax:

create synonym USER_APP.CLIENTS for USER.CLIENTS;


And for every table generation is successful and commit made.
But when I try to use it anyhow on that account, for example:

select * from CLIENTS;


I get an error that CLIENTS do not exist, namely

ORA-00942 : table or view does not exist.


What can I do to fix that or where should I look to determine the cause/solution?
Synonyms have nothing to do with privileges.  They are simply a way to simplify naming.

The error you are getting appears to indicate that user_app does not have privileges on the user.clients table.  You'd need to grant that

GRANT SELECT, INSERT, UPDATE, DELETE
   ON user.clients
   TO user_app;


Of course, in your actual system, I'm guessing that there is a role that you would grant privileges to and that role would be granted to user_app.