FYI To get the project to run from Visual Studio, you need to add several 'existing items' (Add Menu->Existing Item...) to the Slip project including libcrypto-3-x64.dll, PipeReader.dll, Slip.dll, SlipClient.exe, and WinDivert.dll. On each item, make sure to set the 'Copy to Output Directory' option to 'Copy always'. Then when you build the project the items should be copied to your bin folder.
Also, at least in my case, I had to uncheck 'Prefer 32-bit' from the project properties (under 'Build' options)