You see the error as Calendar service request failed (HTTP 503). Retry or contact PK4 if it persists. Reference: 04e46161-7ed8-4403-84e6-c67367dc6e9e.
Connect is failing when the Calendar backend calls Salesforce, before Microsoft sign-in. The service itself is available.
Check the Salesforce user authorized for the PK4 backend connection—which may differ from your logged-in Admin. Its profile needs:
Custom permission:
Use_Microsoft_Calendar_ServiceApex class access:
MicrosoftCalendarApiRequired TimeTracker object and field access
Your Manage_Microsoft_Calendar permission enables the UI but does not grant backend service access.
The log doesn’t expose the underlying Salesforce error, so missing access is a check to perform, not yet a confirmed cause. No permissions or configuration were changed.