To fix the Outlook Error code 0x80040900, modify your Outlook account settings and use the Outlook Inbox tool. Other than that, here are some effective solutions to fix it.
![Upgrade to iCloud for Windows failed error [Fix]](https://i.pinimg.com/originals/98/3a/d9/983ad9190d957c8f8d3c344c0908a688.png)
