Problem with Engage API: visitor history queries will not work (422 - Unprocessable Entity, {"overall":{},"fields":{"starttime":"Required"}})

Hi everyone! I'm trying to use the Engage API to get a visitor's history. The documentation describes that I need to complete this query: https://app.pendo.io/api/v1/visitor/[visitorId]/history?starttime=[milliseconds since the epoch].

I keep getting a 422 - Unprocessable Entity error response back that tells me {"overall":{},"fields":{"starttime":"Required"}}. I've checked the URL I'm using an endless amount of times by now, but I can't make sense of this error. I've tried giving a starttime in seconds and in milliseconds, checked whether the starttime I'm passing actually translates to the correct point in time using epochconverter, checked whether the starttime converts to a string correctly (no decimals), tried different dates....

I've even tried out multiple visitor IDs just in case the real problems was with the ID i chose. The IDs I've tested all work with other queries (like https://app.pendo.io/api/v1/visitor/[visitorId]).

This is an example of what I'm putting in my get request (without a real visitorId): https://app.eu.pendo.io/api/v1/visitor/[visitorId]/history?starttime=1694901600000

Can anyone spot any errors in my URL? Or does anyone have any ideas on what could be going wrong?

Thanks for reading!