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Virto Calendar App stuck on “Waiting for authorization”

Every time Virto Calendar App opens, it signs you in to Microsoft 365 in the background. While it does so, the calendar area shows:

Waiting for authorization

Normally this takes a second or two. If it stays on the screen, or is replaced by Virto Calendar requires to be authorized with an Authorize button, the browser has blocked the sign-in. The message under the heading says why.

The messages and what to do

What you seeWhyWhat to do
Waiting for authorization that does not go awayThe background sign-in loads https://calendar-app.virtosoftware.com in a hidden frame and waits for its answer. The frame did not load or did not answer.Open https://calendar-app.virtosoftware.com in a new browser tab. If it does not open, a proxy, firewall or security tool in your network blocks it: ask your IT team to allow the site. If it opens, reload the calendar page. If every user sees the message at the same time, see the last section below.
Login was blocked by popup blocker. Please add https://calendar-app.virtosoftware.com to allowed sites in Pop-up blocker settings of your Browser.When the background sign-in fails on a SharePoint page or in Teams, the app opens a sign-in window. The browser blocked it.Allow pop-ups for https://calendar-app.virtosoftware.com, reload the page and click Authorize.
Login was canceled by user.The sign-in window was closed before the sign-in finished.Click Authorize and complete the sign-in.
You must enable cookies (including third party cookies) to run the Calendar app.Cookies are turned off in the browser.Turn cookies on, including third-party cookies for the two sites above, and reload.
Login failed: followed by a codeMicrosoft 365 refused the sign-in.Note the code and send it with a screenshot to support@virtosoftware.com.

Users are asked to authorize every time

If the calendar asks people to click Authorize each time they open the page, the background sign-in is failing and the app falls back to the sign-in window. The background sign-in needs cookies from calendar-app.virtosoftware.com inside your SharePoint page or Teams tab, and browsers that block third-party cookies stop it. Allow third-party cookies for your SharePoint domain and https://calendar-app.virtosoftware.com on the users’ computers, or through your browser policy for the whole organization:

Nobody in the organization can open the calendar

If the message appears for every user at the same moment, in every browser, the cause is unlikely to be the browsers. Check first that an administrator has granted the app’s permissions: the app shows “Your global administrator has to consent to the required permissions on behalf of your organization.” until this is done. See Authorization & Permission Request and, if the consent went wrong, Resetting Authorization and Permissions.

If the permissions are in place, write to support@virtosoftware.com with the time it started and a screenshot.

Updated on October 29, 2026