We run feeds through a validator before we can accept shows and add them to our platform. Please try submitting your RSS feed here http://validator.w3.org/ and once there are no errors, try our application process again.
If the validator returns no errors and you're still unable to submit your podcast to Stitcher, please contact our Content Team at: Content@Stitcher.com and provide us with your RSS feed.
We apologize for any trouble and look forward to working with you!
The Stitcher Team