I'm pushing data to a Streaming Data API endpoint using JSON.
In this case, it's just a single channel and a date....
"Temperature": 12.42, "Date": <date stamp in the correct format> }
The interesting thing is that reports work correctly with the data regardless of if I submit my data using lowercase names or uppercase names in my JSON, but dashboards refuse to show streaming data updates unless I'm submitting it in uppercase.
I'd suggest that the subscribe function is case-sensitive, where it would probably be better if it was not - JSON is usually submitted lowercase, but the channel names in PowerBI should allow upper-case names for readability.
At the end of the day it should simply be consistent - either refuse to accept JSON channels that have a different case (which would be very bad in my opinion, but at least it would be consistent), or remove the case-sensitivity from Subscribe (the preferred choice) to allow streaming data to work when there are case differences between the JSON and the configured channels.