Fix Make.com Outlook 500 Error

I already have a Make.com scenario that pulls calendar event details from Vapi, processes them through GPT and a webhook, then tries to post the finished data into Outlook. Everything runs smoothly until the very last step—when the module attempts to create or update the Outlook calendar event, Microsoft returns a 500 error.

Key facts you should know
• Data type in scope: calendar events only—no custom fields involved.
• Webhook is firing correctly and the data payload looks clean when it reaches Make.
• The same flow works flawlessly when the destination is Google Calendar, so the logic and formatting appear sound.

What I need from you
1. Pinpoint the exact reason Outlook (via Microsoft Graph) is rejecting the request.
2. Adjust the Make.com module settings, headers, or payload so events are created/updated without errors.
3. Provide a brief note on any Outlook-specific constraints that caused the issue so I can avoid it in future scenarios.

I can give you instant access to the existing scenario, webhook logs, and sample payloads. Once you patch the error and a test event lands in my Outlook calendar successfully, the job is done.