"Create consents for a single constituent" endpoint failing.

Oliver New

Hi. I would love to implement setting multiple consents for a constituent via this endpoint:

https://developer.sky.blackbaud.com/api#api=cns-cnsnt&operation=CreateConsentsSingleConstituent

However, when I make the request I get the somewhat non-standard error:

The payload I'm sending is:

I have verified that my auth is working OK, for example I can successfully return data from the constituent consent list using a GET request to:
https://api.sky.blackbaud.com/consent/constituents/consents?constituent_ids={id}

Any ideas? Thanks.