To troubleshoot Error 500 in Outlook 365 OWA, you can try the following:

Refresh the Page: Sometimes, the error is temporary. Refresh the OWA page to see if the problem persists.

Clear Browser Cache: Clear your browser's cache and cookies, as cached data can sometimes cause issues.

Try Another Browser: If the error is browser-specific, try using a different web browser to access OWA.

Check Server Status: Contact your organization's IT support or Office 365 administrator to see if there are any known server issues.

Disable Add-Ins: If you suspect add-ins are causing the error, disable them and see if OWA works without them.

Network Troubleshooting: Ensure your internet connection is stable, and there are no network issues causing the problem.

Regards,
Peter

Error 500 is a generic error message that means that the server encountered an unexpected condition that prevented it from fulfilling the request. There are many possible causes of Error 500 in Outlook 365 OWA, but some of the most common ones include:

Corrupted cookies or cache: Outlook 365 OWA stores cookies and cache to help load the website faster. However, if these files become corrupted, it can cause problems loading the website and may result in Error 500. To clear the cookies and cache, follow these steps:

1. Open the browser you are using to access Outlook 365 OWA.
2. Click on the three dots icon in the top right corner.
3. Select Settings.
4. Scroll down and select Privacy and security.
5. Under Cookies and site data, click on Clear browsing data.
6. Select the Cookies and other site data and Cached images and files options, and then click on Clear data.

Outdated browser: If you are using an outdated version of your browser, it may not be compatible with Outlook 365 OWA. To update your browser, follow the instructions for your browser.

Ad blocker: If you are using an ad blocker, it may be blocking the scripts that Outlook 365 OWA needs to load. To disable your ad blocker, follow the instructions for your ad blocker.

Problem with Outlook 365 OWA: There may be a problem with Outlook 365 OWA itself. To troubleshoot this, you can try restarting your browser or clearing your browser's cache.

Problem with the Exchange server: If the Exchange server is experiencing problems, it can also cause Error 500 in Outlook 365 OWA. In this case, you can contact your IT administrator for assistance.

If you have tried all of the above and Error 500 is still occurring, you can contact Microsoft support for assistance.