Upload Product photo

I'm trying to upload photo via OData.

I've started with this code: https://community.creatio.com/questions/how-upload-attachments-odata

and this is where I'm stuck: picture is uploaded but nothing changes (product photo is still empty), as if nothing is saved...

This is the code that I'm using:                           

using (var fs = new FileStream("c:/temp/otter_tiny.jpg", FileMode.Open))
{
    DataServiceRequestArgs args = new DataServiceRequestArgs();
    //Define content type
    args.ContentType = "application/octet-stream";
 
    var productImage = new BPMSync.BpmService.SysImage();
    productImage.Id = Guid.NewGuid();
    productImage.Name = "produtImage.jpeg";
    productImage.MimeType = "image/jpeg";
 
    service.AddToSysImageCollection(productImage);
 
    existingProduct.PictureId = productImage.Id;
 
    //Save changes
    DataServiceResponse responces = service.SaveChanges();
    //Write file stream to activity file
    service.SetSaveStream(productImage, "Data", fs, true, args);
    //Save changes
    service.SaveChanges();
}