Hello,
Upon taking another look at the request, it looks like you are setting the validateOnly header to true. I'm sorry this wan't actually my first question, as it fits the symptoms you're experiencing exactly.
When validateOnly is set to true, the API will validate your request and return any errors with formatting, unknown/invalid IDs or GCLIDs, etc., but it won't actually execute the request.
If you set validateOnly to false, then your request should go through fine.
Regards,
Mike, AdWords API Team