Tracking API submissions "invalid"

Hi. I’m trying to use the Tracking API to submit the contents of log files to our Matomo Cloud instance.
I’m using c#, just because I know it much better than python. I’m submitting the requests correctly, I think, because I get the following results when I submit 8 records:

{“status”:“success”,“tracked”:0,“invalid”:8}

So the submission mechanics seem to be working, but clearly the line items aren’t correct. Is there I a way I can find out what’s making these line items invalid?

Thanks,
kevin