Sorry, Office 365 has been configured to prevent individual acquisition of Office Store Add-ins.

When you saw this error while you try an Office Store Add-in:

Sorry, Office 365 has been configured to prevent individual acquisition of Office Store Add-ins.

In Japanese:

Office 365 は、Office ストア アドインの個人的な取得および実行ができないように設定されています。

Make sure "Let users access the Office Store" is set to On. You can find it in M365 admin center with Admin account > Settings > Settings > Services > User owned apps and services (May 2020):

It may take a few minutes, and may require you to sign-out/sign-in from Desktop Excel App, not Office Store Add-ins.

See also:
* https://answers.microsoft.com/en-us/msoffice/forum/all/office-365-add-ins-error/4e18204b-b8aa-409a-88df-7728328e2eae
* Microsoft Dynamics Office Add-in
* Microsoft PowerApps Office Add-in