Things I have noted while importing bulk via "metrics" API:
1. if i tried import "sleep" and "heartRestRate" all in one json ... I couldn't succeed ... and abandoned the idea.
2. so only on set of data in json ... main interest "sleep":
1. all dates from my data got raised by one day (if my date is 25.01.2021.... imported is 26.01.2021)
2. all 'start_time' got additional 2 hours (if my time is 21:45 .... imported is 23:45)
3. so it all get peculiar if 'start_time' is around 00:00 (midnight)
I imported aprox 220 lines of data ... curl response was also weird (not confirming a success neither failure), but it imported

Any explanation for such behavior?