App management refuses to give me write permissions because my mobile carrier is not supported



I need to write a Twitter Authentication DLL (in C#) for a Twitter desktop client that is used to post tweets. To test this during development, I need to create a test app on and set the permissions as “read and write”. However, it refuses to do so and tells me that I need to register my phone number.

So I went to register my number, but it tells me that my carrier is not supported.

What is happening? How do I get write permissions so that I can do my job?