How do I fix a 403 error with C# when trying to access SharePoint

Question

Using the Microsoft.SharePoint.Client namespace in a C# code, I am trying to access a SharePoint List but I am getting a 403.  Is it because the Microsft List I am trying to access is on a different computer on the internet and the program has to be on the same "ecosystem"?  Is there a way around this?

Answer 1

may i know what environment it is? is it online of on-prem?

Answer 2

It is on prem.

But I think the security set up is so tight that it is not possible.

I am thinking of solving this using Firfox Selenium