how to upload image on flickr using asp.net

it sounds looks like follow check some option or try another link..

Have you set a callback URL on Flickr? You need to edit the API key settings and tell it where to redirect back to after you have authenticated.

or

This setting is not inside the plugin. It is on Flickr.com. Go to Flickr.com. After you login, go to Your Apps from the You menu on top. You will see your Flickr app. Click this app. Then click Edit Authentication Flow. Here you will find a setting called Callback URL. Set this to your wp-admin/ URL

or  hit this link.
https://wordpress.org/support/topic/plugin-awesome-flickr-gallery-oops-flickr-cant-find-a-valid-callback-url

try this link

http://amitpatelit.com/2013/01/08/upload-photo-in-flickr-by-asp-net-code/

and official link..

https://www.flickr.com/services/apps/create/