Flow Approvals - Actionable Cards in outlook (not working?)

Cross posting (cc Robert Tracey):

https://techcommunity.microsoft.com/t5/Office-365/Flow-Approval-via-Email/m-p/216295/highlight/false#M14501

We cannot get the Flow Approval actionable messages to work in Outlook, we get the following error when running it through the debugger add-in for Outlook:

Does anyone have any insight into what this error means and how we can fix it?  These are out of the box Flow Approvals with no customization whatsoever.