An unfamiliar appointment appears between genuine meetings. Its title says you have won something or must resolve an urgent account problem. Appearing in a calendar does not prove that the organiser is trustworthy, even when the invitation uses the name of a familiar company.
Do not use the invitation as the verification channel
Leave links, attachments and telephone numbers inside the suspicious event alone. If it claims to concern a service you use, open that service through a known app or an address you already trust. Check for the alleged problem there.
A sender display name is easy to misread as a verified identity. Inspect details only through the calendar interface, and do not assume that a familiar logo or plausible meeting description establishes a relationship.
Use the service’s own controls
Google Calendar’s guidance on unwanted invitations explains controls for limiting which invitations are automatically added and for reporting spam. Other providers use different settings. Follow the instructions for the account where the event appeared rather than applying a screenshot from another calendar service.
Be aware that restricting automatic additions may also affect legitimate invitations from people you have not previously contacted. Review pending invitations through the trusted interface so a useful security setting does not silently disrupt your work.
If you already followed a link but entered nothing, close it and avoid further interaction. If you entered a password or approved an unexpected sign-in, use the service’s official account-recovery and security process promptly. Review the account from a trusted device, not from the invitation’s landing page.
For a work account, report the event through your organisation’s normal security channel. Include the relevant event details without forwarding a dangerous link to colleagues as a warning. A calendar entry is a request for attention; it is not evidence that the request deserves your trust.