Power Platform Community Forum Thread Details

I'm trying to building on an existing flow to add people to an existing event without notifying everyone already invited. I have found and followed the flow at Power Automate Add Attendee To Meeting And Don't Email Others.

First I use the Get events (V4) action to get the event in question, which is in a shared calendar.

Then I initialize the two variables varCalendarId and varEventId.

varCalendarId Value =

actions('Get_events_(V4):_Test_Event_2025')?['inputs']?['parameters']?['table'] 
varEventId Value =

first(body('Get_events_(V4):_Test_Event_2025')?['value'])?['id']
Then I try to send an HTTP request to get the event information.
URI = 
https://graph.microsoft.com/v1.0/users/calendars/@{variables('varCalendarId')}/events/@{variables('varEventId')}
This is where it falls over in testing. The preceding steps work as expected, and produce the expected results, but the flow fails on Send an HTTP Request: Get Event, with the following error:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN""http://www.w3.org/TR/html4/strict.dtd">
<HTML><HEAD><TITLE>Length Required</TITLE>
<META HTTP-EQUIV="Content-Type" Content="text/html; charset=us-ascii"></HEAD>
<BODY><h2>Length Required</h2>
<hr><p>HTTP Error 411. The request must be chunked or have a content length.</p>
</BODY></HTML>
 
Incidentally I have tried the same process with an event created in my own calendar and used the URI
https://graph.microsoft.com/v1.0/me/calendars/@{variables('varCalendarId')}/events/@{variables('varEventId')}
Got the same result and error.
 
The post and comments at Power Automate Add Attendee To Meeting And Don't Email Others suggest that this should work, can someone suggest what I'm doing wrong?