HTTP status codes are documented here.
403 Forbidden errors are returned when the user does not have sufficient permissions to perform the requested operation. The request should not be repeated.
In other words, your user account is not entitled to run those TRTH queries. Are you sure it is permissioned for TRTH data ? You might want to contact your Thomson Reuters account manager to check that.
PS: the syntax of all 3 of your requests is correct.