There can be several reasons why a callback handler doesn’t work, although this is usually because the handler isn’t contactable for some reason. To check if your handler logic works you can test it using our callback handler test tool. If your callback handler still doesn't work you should check that none of the following problems apply.
The first potential problem is that the callback URL passed to the save method is incorrect, if the domain is incorrect it could result in the error you are trying to use a Callback URL that does not exist! Please enter a URL that is both absolute and public.
The second potential problem is that the URL maybe invalid, it may be in the wrong format or a non-public, local URL. In this case it should show the error message: Invalid Callback URL. Please provide a valid web address.
The third potential problem is that the web host may be blocking requests from GrabzIt. This can sometimes happen if you have been requesting a large number of captures resulting in a large number of callbacks that some hosting companies can misinterpret as a Denial of Service Attack.