If you see the following message in your calendar after logging in, you are using an email address that is not registered as a login address for this account.
Solution 1) Find the correct address
Basically, you can log in with all logins that are registered under Settings > Employees > Permissions.
Contact the owner of the company and ask them for the correct email address that you can use for login.
Solution 2) Add email address
If you wish to have a new address registered for login, you can inform a person who has the necessary permissions to do so. Under Settings > Employees > Permissions, additional email addresses can be added, which can then also be assigned the desired permissions. Learn more about creating employee logins here.
Solution 3) Check login permissions
If the address you are using is already registered and you still cannot log in with it, it may be that no permissions have been assigned to the login. Ask a person who has the necessary permissions to check under Settings > Employees > Permissions and add permissions if necessary.