Using the Amplitude Dashboard REST API, I am attempting to get a count of all unique times a custom event was triggered with a filter of a custom event property. However I am unable to even get the simplest event segmentation to run, though all other endpoint hits (except Funnels which also use the e event parameter) are working as expected. In other words, my auth is working and I'm able to successfully get data from all the endpoints that don't require the e event parameter.
Here is an example of a constructed endpoint using event segmentation that is as simple as I believe it could possible be and which is failing with a 400 error.
https://amplitude.com/api/2/events/segmentation?e=\{"event_type":"_active"\}&start=20170401&end=20170402
While the call I want to do is ultimately more complex and involves a filter, I'm unable to just get this call which is one of the simplest event segmentation calls possible, considering the e, start, and end parameters are all required.