Facebook page leadgen webhook returns error 102 Server Failure

I know this is really old but I came across the same issue and this is what I found.

"You can use this tool to create and delete test leads for your forms; however, you cannot use the tool in developer mode."

Basically saying you will get that 102 message if you're in dev mode, which makes no sense why they would have a testing tool you can only use when your app is "live".

One recent change (as of May 1, 2018) is that the app Status must be "Live" in order to receive actual webhook updates. If it is left "In Development", webhook requests will now fail with error code 102 "Server failure" (such a helpful message!), and the Webhooks page for the app (https://developers.facebook.com/apps/{your app ID}/webhooks/) will show a message saying:

Applications will only be able to receive test webhooks sent from the app dashboard while they are in development. No production data, including that of app admins, developers, and testers, will be delivered unless the app is live.

It took me a while to figure that out since the webhooks had been working previously. Hope this helps some people!