Pyas calendarsMicrosoft Graph v1.0 refuses link attachments on Outlook events
Updated
TL;DR
Adding a link attachment to an Outlook event through Microsoft Graph v1.0 failed every time we tried, on Outlook.com and Microsoft 365, with the error "The property '' is required". The property that holds a link attachment's URL exists only in Graph's beta API. Upload the file as a file attachment instead, or put the link in the event's description.
What we saw
Outlook supports two kinds of attachment on an event: a file, stored with the event, and a reference to a file somewhere else, such as a document link.
Observed on Outlook.com and Microsoft 365, 2026-10-26
Every attempt to add a link (reference) attachment to an event through Graph v1.0 was refused with "The property '' is required", on Outlook.com and on Microsoft 365 alike.
The error names no property, which makes it hard to diagnose.
Why it happens
The field that carries a reference attachment's URL is only defined in Graph's beta endpoint. On v1.0 there is no way to send it, so the request is missing a required property that the v1.0 schema cannot name.
What to do
- Upload the file as a file attachment when you have it.
- Put the link in the event's description when the file lives elsewhere and should stay there.
- Use the beta endpoint only if you accept its terms. Microsoft does not support beta APIs in production apps, and they can change without notice.
How Pyas handles it
Pyas refuses a link attachment on Outlook with a clear VALIDATION_UNSUPPORTED_OPERATION error and a hint to upload the file instead, so you don't get Graph's unnamed property. Outlook events in the sandbox behave the same way, so you find out while building.