As I understand it, minutesAgo is a measurement of time and cannot be a metric, because it cannot be aggregated in any way by default.
Imagine that you expand the country by country (dimensions = rt: country) ... and there are N visitors from one country that came to your site in the last 10 minutes. What would be the value of minutesAgo? average? last?
Metrics must be aggregate so that they can be metrics. Time values ββin OLAP databases, as a rule, do not have this property (in essence), therefore they are better modeled as sizes (usually by periods: "day", "week" ... or in this case "minutesAgo").
As @Pete already mentioned, in this case you can apply a long combination of filters (or regular expression) and use totalsForAllResults :
"totalsForAllResults": { "rt:totalEvents": "2" },
jjmontes
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