Exchange Service

This error message means you have to setup Autodiscover with your Exchange server.

The autodiscovery field (in your exchange server settings) needs to be populated with an address that ends with: "EWS/Exchange.asmx".

After setting up your Autodiscover and you are still receiving an error message, please follow the following instructions:

1) Perform an Autodiscover test to make sure it is properly set up. Click here.

2) If the Autodiscover test failed, please get in touch with your IT department or consult your Exchange server certified tech for assistance for troubleshooting.

Once you're setup with Autodiscover, please try logging in again.

Please mark as "Accept the answer" if the above steps helps you. Your suggestion will help others also !

If its a new tenant then Basic Authentication will be disabled by default (and you shouldn't re-enabled it), I would say as a start read through https://learn.microsoft.com/en-us/exchange/client-developer/exchange-web-services/how-to-authenticate-an-ews-application-by-using-oauth create an EWS App and use the samples provided.

If your building an Application that is going to only access Office365 then you don't need Autodiscover which is what the example in the above link show, if you are going to have Hybrid on OnPrem then you do want to use Autodiscover.