Problem embedding report - "This content isn't available"

Having recently waded through this labyrinth of configuration, I'll share the parts I got stuck on in hopes that they help you find your solution:

- embed tokens are only required if you're using the Premium capacity approach.  Premium capacity is required if your end-users (that is to say, the people viewing your embedded content) do not have Power BI Pro licenses and are not a part of the Power BI Workspace that is hosting your datasets, reports, dashboards, etc.  If your users have their own Pro licenses (sometimes the case if you're sharing internal data with colleagues) and are a member of the source Workspace, you won't need an embed token - JUST your access token.  (It sounds like you're up to speed on access tokens, but let me know if I can expand on those.)

- the bug that plagued me right up until I got embeds working was the TYPE of authentication I was specifying in my request.  I'm taking the Javascript route, but you should be able to figure out what the C# equivalent is: 

                var models = window['powerbi-client'].models;
            
                var config = {
                    type: 'report',
                    tokenType: models.TokenType.Aad,
                    accessToken: accessToken,
                    embedUrl: reportEmbedUrl, 
                    viewMode: models.ViewMode.View,
                    id: reportId,	
                    
                };

Every example I found here and elsewhere on the internet was using "tokenType: models.TokenType.Embed" - which is intended for use with the method I described above.  I was using the Active Directory Authentication Library (adal.js) approach, which checks the user's browser for existing AD sessions (recommended for the end-user-has-Pro-license approach).  When I finally tried dumping "models" to output and saw the parameters model.TokenType accepts, it all came together.

Happy to share my working code if you think it will be of use, but hopefully the above will get you started toward the right solution.  Good luck!