Help getting AAD Token for embedding report.

Hello everyone. 

I'm new to embedding using authentication tokens, and I'm also not the best at coding, so I'm pretty lost with this and have run into errors that I cannot figure out. There seems to be quite a few guides out there, but a lot of them are outdated, I seem to have made the most progress with this one: https://docs.microsoft.com/en-us/power-bi/developer/embed-sample-for-customers

I'm stuck now at a part where I am getting an error after launching code in visual studio. 

I tried googling variations of "PowerBIEntityNotFound" and haven't stumbled upon any solutions that have helped me. I feel like it shouldn't be this hard to get a AAD token and that I'm missing something here. Any help would be appreciated.