There could be a couple of reasons why your add-in isn't launching. For example, your company firewall might be preventing you from using external add-ins, or you might not have the correct permissions enabled in Internet Explorer.
Please refer to this Microsoft documentation to find out what your specific error message means: https://docs.microsoft.com/en-us/office/dev/add-ins/testing/testing-and-troubleshooting
If the add-in is blank or just loading, you could try clearing the browser cache on your computer.
For Mac, you need to clear the browser cache in Safari and for Windows, you need to clear the cache in Internet Explorer (not Microsoft Edge).
Guides:
Clearing cache in Safari: https://clear-my-cache.com/apple-mac-os/safari.html
Clearing cache in Internet Explorer: https://clear-my-cache.com/windows/internet-explorer-11.html
Troubleshooting Error Messages