I've been at this on & off for a few months now. Relevant info:
- HFL in AGO; 'Keep track of changes to data' enabled.
- Have tried several different flows based on blog posts etc., some of the previously provided examples from Esri appear to be out of date now as things have advanced (such as parsing an array).
- The trigger 'When a record is updated in a feature layer' is working.
- The action 'Fetch update, changes, or deletions...' returns an empty payload regardless of the changes made to the HFL (delete, update attributes, etc).
- While the flow shows as successful, any of the subsequent steps like posting in a teams channel actually just hang
Below are screenshots showing the different flows:
Using 'body'

Using array(triggerOutputs()?['body']) per a previous Esri example:

Created a parallel branch to test the trigger itself and this works as expected:

As we can see the trigger is firing as expected:

and the subsequent Teams channel message is sent.
But for the Fetch updates, changes, or deletions, the payload/body/output is always empty in all these versions:

What am I doing wrong??