How to activate a Microsoft Office 365 key?

Activating a Microsoft Office 365 key is really simple, just follow these steps:

1. Go to https://setup.office.com/,
2. Sign in to your MS account (or register a new one),
3. Redeem the key at https://microsoft365.com/setupbusiness

The key is not working

If you have activated the key according to the guide but the code appears not to work, please check what type of error message you receive and depending on it follow the appropriate instructions:

• My key is Duplicated / Already Used. How can I proceed?
• My key is Invalid. How can I proceed?
• My key is region locked / can't be activated in my country. How can I proceed?
• My key activated a different product that it was supposed to. How can I proceed?
• The key I bought didn’t activate all of the content it was supposed to. What can I do?