Zoho Books Webhook Request Format

Zoho Books Webhook Request Format

I have created a webhook and workflow for Expense, Invoice, and Payment modules on create/edit events. Settings for each are as follows :

Include HTTP Headers - Content-Type = application/json
Append All Parameters

I can view what I assume is the request sent to the registered url in the Workflow Logs, but when the endpoint is hit, I have an invalid model state. When using the json object from workflow logs to test locally, everything works as expected. 

Does anyone know what might be causing this? Did I configure something wrong? Is the workflow log not the actual request being send to my service?