The most common reasons for this are you are trying to log in using a Login Account that the Username has not been set up for (there 3 Accounts: Katipolt Account, Continue with Google and Continue with Microsoft) OR you have misspelled the email Username.

To Resolve: Check you are using the Login Account the Username was set up for OR create a Katipolt Account (the recommended Account) for the Username (you can use the same Password) OR check the spelling of the email Username you are using.