We have been contacted by Ebay stating that they may close our account because we have not implemented deletion/closure notification webhooks. The trouble is our software is running on .net 4.0 and we are not using Rest Api's instead we are using a web reference to com.ebay.developer. I thought I might get away with just adding an extra class with those methods on and make them restful, but When I try and use the challenge response code that they say we should be using, it uses the IncrementalHash class which didn't kick into the cryptography library until much later, so again I'm in a bit of a quandary. Because of the way the code has been written it's not as straight forward as just upgrading the framework. Any ideas how I can move forward without doing a whole rewrite and upgrade would be welcome.