WeTransferClient wt = new WeTransferClient ("your api key here");

// Authorize your WeTransfer app, this call the /authorize endpoint
await wt.Authorize ();

// Create Partial File Information so WeTransfer knows how many files
// you're going to upload, the names of those files and their sizes
PartialFileInfo [] partialFileInfos = new PartialFileInfo [1];
partialFileInfos [0] = new PartialFileInfo
{
    Name = "TestFile.png",
    Path = "/path/to/the/file/TestFile.png",
    // Size of the file in bytes
    Size = 48570239
};

// Create a File Transfer which informs WeTransfer that you're about to upload files
// The second parameter is the transfer message which will show on the download page
FileTransferResponse response = await wt.CreateTransfer (partialFileInfos,
                                                         "Test Transfer");

// Now you can upload the files!
// The first parameter is the transfer's ID
await wt.Upload (response.ID, response.Files);

// Now you need to tell WeTransfer that your files have been uploaded
FileUploadResult result = await wt.FinalizeUpload (response.ID, response.Files);

// FileUploadResult contains the url to the download page and the date of the expiry