@Dawid_Nguyen

Go to .nuget folder and delete the folder with this name and then try reopening the project

Cheers

Let us know for a more individually guidance folowing:

@Dawid_Nguyen

Inside the .nuget folder…you will have packages folder…which containa folder with name system.web.http please delete that and reopen the project and check

Cheers

let us know on which class you are interrested. As shown above it was resolved without explicit addition to the dependencies

At least try it