In the second half of 2021, Microsoft stopped supporting Basic Authentication for Exchange Web Services (EWS) to access Exchange Online. Basic Authentication was replaced with Modern Authentication (based on OAuth 2.0). For more details, please see Exchange Online deprecating Basic Authentication - Microsoft Lifecycle | Microsoft Docs.
Starting from the 8.3.0 version Cayosoft Administrator uses only Modern Authentication and requires Exchange Online PowerShell Module (EXO V2). Exchange Online PowerShell connectivity still requires Basic Auth to establish the connection. From the Microsoft article: "The username/password isn't sent to the service using Basic, but the Basic Auth header is required to send the session's OAuth token, because the WinRM client doesn't support OAuth. We are working on this problem and will have more to announce in the future. Just know that enabling Basic on WinRM is not using Basic to authenticate to the service." For more details please see this Microsoft article: Deprecation of Basic authentication in Exchange Online | Microsoft Docs.