calcom/cal.diy · error · InternalServerErrorException

Unable to fetch connected calendars events. Please try again

Error message

Unable to fetch connected calendars events. Please try again later.

What it means

Thrown by CalendarsService.getBusyTimes (calendars.service.ts:126) as InternalServerErrorException (HTTP 500) when getBusyCalendarTimes(...) returns { success: false }. The upstream Cal.com platform-libraries call could not fetch busy times from one or more providers; the underlying error detail is not propagated to the caller (diagnosability gap).

Source

Thrown at apps/api/v2/src/platform/calendars/services/calendars.service.ts:126

    userId: User["id"],
    dateFrom: string,
    dateTo: string,
    timezone: string
  ) {
    const credentials = await this.getUniqCalendarCredentials(calendarsToLoad, userId);
    const composedSelectedCalendars = await this.getCalendarsWithCredentials(
      credentials,
      calendarsToLoad,
      userId
    );
    const calendarBusyTimesQuery = await getBusyCalendarTimes(
      this.buildNonDelegationCredentials(credentials),
      dateFrom,
      dateTo,
      composedSelectedCalendars
    );
    if (!calendarBusyTimesQuery.success) {
      throw new InternalServerErrorException(
        "Unable to fetch connected calendars events. Please try again later."
      );
    }
    const calendarBusyTimesConverted = calendarBusyTimesQuery.data.map(
      (busyTime: EventBusyDate & { timeZone?: string }) => {
        const busyTimeStart = DateTime.fromJSDate(new Date(busyTime.start)).setZone(timezone);
        const busyTimeEnd = DateTime.fromJSDate(new Date(busyTime.end)).setZone(timezone);
        const busyTimeStartDate = busyTimeStart.toJSDate();
        const busyTimeEndDate = busyTimeEnd.toJSDate();
        return {
          ...busyTime,
          start: busyTimeStartDate,
          end: busyTimeEndDate,
        };
      }
    );
    return calendarBusyTimesConverted;
  }

View on GitHub (pinned to 176037d0af)

Solutions

Retry with exponential backoff — many failures are transient provider hiccups.
Check provider status pages and verify the user's OAuth token validity (re-connect if revoked).
Narrow the dateFrom/dateTo range and reduce the number of calendars in calendarsToLoad.
Inspect server logs (platform-libraries integration) for the actual failure cause, since it is not in the response.

Example fix

// before: single shot, surfaces only a generic 500
const times = await api.get('/v2/calendars/busy-times', { params });

// after: bounded retry with backoff on 500
async function getBusyTimesSafe(params, attempts = 3) {
  for (let i = 0; i < attempts; i++) {
    try { return await api.get('/v2/calendars/busy-times', { params }); }
    catch (e) {
      if (e.response?.status !== 500 || i === attempts - 1) throw e;
      await sleep(2 ** i * 500);
    }
  }
}

Defensive patterns

Strategy: retry

Validate before calling

// Reduce blast radius before calling busy-times
const safeCalendars = calendarsToLoad.filter(c => ownedIds.has(c.credentialId));
const clipped = {
  ...params,
  dateFrom: max(params.dateFrom, todayMinus(60)),
  dateTo: min(params.dateTo, todayPlus(60)),
  calendarsToLoad: safeCalendars,
};
await api.get('/v2/calendars/busy-times', { params: clipped });

Type guard

function isBusyTimesSuccess(res) {
  return res?.success === true && Array.isArray(res?.data);
}

Try / catch

async function getBusyTimesRetry(params, attempts = 3) {
  for (let i = 0; i < attempts; i++) {
    try {
      return await api.get('/v2/calendars/busy-times', { params });
    } catch (e) {
      if (e.response?.status !== 500 || i === attempts - 1) throw e;
      await new Promise(r => setTimeout(r, 2 ** i * 500));
    }
  }
}

Prevention

Retry 500 busy-times failures with exponential backoff — many are transient.
Keep dateFrom/dateTo ranges modest to avoid provider timeouts/quota.
Log the underlying integration error server-side; the HTTP message intentionally hides it.

When it happens

Trigger: Provider (Google/Microsoft/Apple) API outage or rate limit; an expired OAuth token causes a provider 401 surfaced as failure; malformed/huge date range; network timeout to the provider.

Common situations: Google Calendar API quota exceeded; token refresh failed inside the integration; transient network blip; very wide dateFrom/dateTo window.

Related errors

AI-assisted analysis of calcom/cal.diy@176037d0af (2026-08-12). Data as JSON: /api/errors/91bdb0ba09624a95. Report an issue: GitHub.