Thanks for getting back at me @rchoi. It’s hard to provide a self-contained sample code but I’ll try to give you every info you need.
I uploaded a couple of files to my OneDrive so you can see what I’m seeing with Fiddler.
Here’s what I get when I try to send the raw file: http://1drv.ms/1KKVxqE
And this is the one in base64: http://1drv.ms/1KKVyLe
In both cases I get the error from the subject.
I also tried to use twurl in order to see what is it sending but I get another error
(mentioned here: https://github.com/twitter/twurl/issues/58)
Here’s the pic I’m trying to upload. please let me know if there’s anything I can help you with in order to help me.
