API Issue: Metric-Aggregate dimensions returning empty strings for custom metric

Hi,

I am experiencing an issue with the Metric-Aggregate API (POST /api/metric-aggregates/) regarding the internal metric added_to_list_internal_klaviyo (Metric ID: YbGwiU).

The Problem: When I query this metric and attempt to group by "List", the API returns the correct total count, but the dimensions array contains only an empty string "".

The Evidence:

1. I have verified via the Events API that these events do contain the properties "List ID" and "List Name" within the event_properties object.

2. However, attempting to use "by": ["List ID"] or "by": ["$list_id"] in the aggregate request results in a 400 Invalid Input error, stating these are not valid choices for by.

My Request: Could you please clarify why these properties—which clearly exist on the event level—are not available as dimensions for aggregation on this specific internal metric?

Technical Details for your team:

• Metric Name: Added to List

• Metric ID: YbGwiU

• Integration: Klaviyo (Internal)

• Environment: Production 2026

Thank you for your assistance.