The problem is that you need to use work account (xxxx@xxxx.onmicrosoft.com) with Office 365 for Business subscription. Personal accounts with Office 365 for Home subscription cannot be used to edit documents this way.
If you have a personal account with Office 365 for Home subscription and you want to edit documents in the cloud, select Edit in MS Office Online option.
Then click Edit Document > Edit in Browser.
Edit document using MS Office Online.
Don't forget to save file in Bitrix24 window.