Webhooks with GameSparks

Hi, Im trying to setup webhooks with GameSparks I have my url setup like this:

https://preview.gamesparks.net/callback/286806FRSf6P/photonHook/LPXRvTNnut3n20N1RTDgEfsJ13zaxjL5/?path=GameCreate?

The problem is in unity Im getting errors for example:
OnEvent: Event 251: {(Byte)218=(String)Failed to forward request to https://preview.gamesparks.net/callback/286806FRSf6P/lBdmFptAC0V2wjxYFqGYlUScSYA7W3P9/?path=GameCreate? : 'Expectation Failed' httpcode=417 webstatus=7 response='', HttpQueueResult=5., (Byte)254=(Int32)0}

I managed to setup webhooks with BrainCloud but now I want to move to GameSparks but I have tried everything, not sure what Im missing.

Any ideas?

Thanks