I am trying to follow a yt tutorial https://youtu.be/OLBmtRFFwcQ?si=MIb_Y9mXzgGpk51y at around 8 mins, I encountered this problem

after a quick bing search it says that I am missing something in my Visual studio, idk what it is and kinda stuck in this problem now, just a newbie in this backend stuff please be considerate :>
I already fixed this problem by rebuilding the solution and updating NuGet packages.