C#: Fix code (API request to a website)

Dear freelancers, I need help fixing a small project. My C# code makes an API request to a website, but the authentification method changed from user/password to a "random token". That's all I could learn. I do not have API documentation. If you want to try to fix it, you are welcome. Maybe it needs a few hours. If you are succesful, I have more project you could work on. Thanks