Issue with Uploading Document to Windchill via C# Code – contentInfos Empty

I have set up the code this way with the aim of successfully uploading a document to Windchill using Postman, which works fine. However, when I convert this to C# code, I don't get any errors, but in stage2, the contentInfos is coming up empty. The same data in Postman is coming through filled. I suspect the issue is in the file upload part, but I can't think of a solution. Even though I have downloaded the incoming file to a folder and provided the file path, contentInfos is still empty. Because of this, I am unable to upload the WTDocument through the code. Can you help me with this?