The Reply URL is a URL from which your application must be served. When authenticating the current user with the authorization code flow, Azure AD will only redirect the user in the browser to a registered reply URL to provide your application with an authorization code that is used to redeem an access token. It will not work correctly if your application has not registered the reply URL for the application itself. When testing and debugging in Visual Studio, make sure to use SSL so you have a reply URL such as https://localhost:44300.
How are you implementing the authorization code flow with Azure AD? The recommended approach is to use ADAL.NET and the OWIN components for Cookies and OpenIdConnect. Is this what you are using?
Thanks @TedPattison - I am basically authenticating using Office 365 Power BI Pro license. I am new to Embed concepts - do I absolutely need to have Azure AD? My use case involves trying to embed Power BI reports in a .Net application web page, with the organization users using their Office 365 Power Pro accounts for authenticating and viewing the embedded reports.
In the sample solution I did put http://localhost:13526 as my default redirect URL, still I see the error. Is SSL required in development/testing?
Please let me know if I am misundrstanding something or need to do any additional step. Thanks