What is the proper way to query datetime field?

[mongting]

One of our project goals is to filter time-series data within the specific time interval.

I see that OBS collection of Demo server includes datetime columns in the csv file.

https://demo.pygeoapi.io/master/openapi?f=html#/obs/getObsFeatures

I tried to query dateTime on OBS but it doesn't seem to work.

1. This should return one row but it returns all of the five rows.
   https://demo.pygeoapi.io/master/collections/obs/items?f=json&lang=en-US&limit=10&skipGeometry=false&offset=0&datetime=2001-10-30T14%3A24%3A55Z

2. This should return two rows but it returns all of the five rows.
   https://demo.pygeoapi.io/master/collections/obs/items?f=json&lang=en-US&limit=10&skipGeometry=false&offset=0&datetime=2002-10-30T18%3A31%3A38Z%2F2003-10-30T07%3A37%3A29Z

I tried every example of "8.2.1.2. Parameter datetime" in OGC API documentation. ( https://docs.ogc.org/is/19-086r5/19-086r5.html#toc28 )

But none of the queries filters the dataset of OBS.

Is this a bug or do I have to query the datetime differently?