It is Unix Timestamp, provided with 4 extra digits after the second unit digit (i.e. values are in hundreds of microseconds, instead seconds as expected).
Try 1601629220 instead 16016292200000 in any timestamp to date converter (e.g. here): you should get "Friday 2 October 2020 09:00:20"
No, trial just returns data from random coordinates, but it should work. I have just tested it and it works for my trial key. Can you provide me with more details? Any body in the error? Your request body (please do not publish yout API key)?