How to add user custom action on top level root site collection in SharePoint Online?

Question

I have a SharePoint Online environment as https:///domain.sharepoint.com.

Now I am trying to add custom JS codes to the site page in the above specified site. Whenever I try to add the code on top level root site it always throws error:

Access denied. You do not have permission to perform this action or access this resource.

FYI: I am the owner of the tenant.

Also when I tried opening top level root site using SPD, there also I got the same error.

So, I want to know whether its possible to add some custom codes on the top level root site collection?

If its possible then how we can achieve this?

Answer 1

Go to SharePoint online admin center > Settings.

In the custom scripts section, ensure that you have turned on the scripting capabilities as below:

Once this is done, click on Save at the bottom.

Now, open SharePoint online PowerShell and run the below command(use the SharePoint admin account) :

Set-SPOSite "https://domain.sharepoint.com" -DenyAddAndCustomizePages 0

Now, you should be able to add custom scripts/user custom actions in your site collection.

By default, in a new tenant:

1. For personal sites, custom scripting is disabled by default.
2. For self-service created sites, custom scripting is disabled by default.
3. For the Root Site Collection of the Tenant, custom scripting is disabled by default.

By changing the above setting and running the Powershell command, we will enable the scripts for the root site as well.