To resolve the problem you will need to confirm the registered redirect uri matches what you are submitting in your request.
1. Login to OAuth manager
2. Locate the OAuth client you are using to submit the request and click 'List Keys'
3. Click the 'Edit' button on the client key
4. Locate the field for the 'Callback URL'. This must match what is submitted with your request. If needed you can also update the URL here as well.