Klaviyo's Metrics endpoint does not provide a method by which you can easily fetch events (metrics) within a specified date range. The metrics/{metric_id}/timeline endpoint takes a ‘since’ and a sort parameter. What is not well documented is that the sort parameter manipulates the returned data in two ways as it defines the direction and also the side of the ‘since’ parameter for which data is returned.
The best way to illustrate this is a request without a ‘since’ parameter (defaults to now) and toggling the sort parameter (defaults to desc). The default request without either param specified returns all events (paginated) before the ‘since parameter’ (now, the time of the request). A request with only the sort parameter set to "asc" will return an empty array because there are no events that can be returned after the ‘since’ parameter (these events are in the future and haven't been recorded yet).
Alternatively, you can export aggregated event data by using the metrics/{metric_id}/timeline endpoint for specific time ranges.
For the api endpoint reference, please see here: https://www.klaviyo.com/docs/api/metrics#metric-timeline
