The class CkUpload fails to add the Authorization header, using the AddCustomHeader method. You can add other custom headers but not the Authorization header.
For example,
CkUpload upload;
upload.AddCustomHeader("Authorization", "Bearer <token>");
You can verify it with the method UploadToMemory, which prints the whole request, lacking said header.
I'm using Chilkat version 9.5.0.95, C++, on Windows, with MS Visual Studio 2022.
This will be fixed in v9.5.0.96, to be released at the end of this month.