If the email address that was entered during login, is not an agent/contact in the account, then this error would be displayed. You could sign up for a new account, using the Sign Up option on the Portal, or ask to be added as an Agent from under Admin-->Agents in your account. Once this is done, you can login to your Freshservice Account.
If you continue to face issues with login, reach out to our support team through [email protected] for further assistance.