By default, script is allowed on most sites that admins create. It is not allowed on OneDrive, on sites users create themselves, on modern team and communication sites, and on the root site for your organization. You’ll probably want to limit the amount of script you allow for security reasons. For more info about the security implications of custom script, see Security considerations of allowing custom script.
There are two approaches for achieve this. In this post, we will cover the first one by going to the SharePoint Admin Center.
You must be a SharePoint global admin to perform this action.
Enable Custom Script
Go to the SharePoint Admin Center. https://<domain name>-admin.sharepoint.com. In this link, replace <domain name> with yours. The Admin Center looks like below screen.
Click on Settings and click Classic Settings Pane.
Scroll to the bottom to find Custom Script. Select Allow users on both the radio button. Please note that changes to this settings might take up to 24 hours to take effect.
In the next post we will cover another approach that will instantly enable the custom script.