Response from Mixpanel;
Hi Dahne,
Julianne from Mixpanel Support here- thanks for reaching out about this.
Diving right in, the event aggregate API endpoint can only return values for actual raw data, so it would expect an actual event that has been tracked. It isn't able to return data for custom events- apologies for not having better news there. I've gone ahead and filed a feature request on your belhalf around custom events in the APIs.
One option to get custom event data would be to create and save a report with the information that you're interested in. From there, you could use the Query API to query for the saved report.
Please let me know if anything above needs further clarification. Looking forward to your response!
Best,
Julianne
Support Engineer | Mixpanel