Adobe Workfront Document Webhooks - Any experiences?

Hello community,

Is there anybody here who has made some experiences concerning the Adobe Workfront Document Webhooks to integrate an external document provider?

I know, this is a quite old "feature", which does not seem to be actively worked on, but I hoped, that at least the basic functionality would work. 

I started using this documentation, but although my middleware provides valid JSON, I do get the following error message:

Cannot deserialize the response message

I there is anybody out there having experiences with this, I would be glad, if you could share some insights.

Thanks in advance.

Regards

Lars