Please follow this article to enable custom scripting for your SharePoint Online environment
The majority of KWizCom apps for SharePoint Online require a feature called custom scripting to be enabled. Without it, the app will display an error message when attempting to configure the app settings.To enable custom scripting, click on the admin button
in the top left of the page > then click on Admin > Admin centre > SharePoint > Settings. From there, scroll down to the Custom Script section and select the option "Allow users to run custom script on..." for both personal sites/self-service created sites.
Note: It may take up to 24 hours before this setting is updated on your sites
For more information: