Mirage `passthrough` is not working

I'm trying to use passthrough for a POST request in this Ember project

this.passthrough('/thirdeye/entity?entityType=ANOMALY_FUNCTION');

This is what the call looks like in app/mirage/config.js. I got the following error:

Mirage: Your Ember app tried to POST '/thirdeye/entity?entityType=ANOMALY_FUNCTION',
but there was no route defined to handle this request.
Define a route that matches this path in your
mirage/config.js file. Did you forget to add your namespace?

Clearly, I've added that call to the config file, but it's not being picked up. I read that passthrough only works for >= jquery 2.x, which my project is.

Does anyone know what else could cause this?