Removing Deny permission on Add and customize pages

In all relatively recent site collections you will find a Deny permission on Add and customize pages. This permission rule prevents changes to site pages as a security measure. Unfortunately, it also means that you won't be able to customize your classic list forms using Ultimate Forms. The classic forms section will be either disabled or completely hidden from the user interface.

1. If you haven't done so, install SharePoint Online Management Shell
2. Run the following commands, replace (for example, if your site is https://example.sharepoint.com, your tenant name is "example", so the full tenant URL would be https://example-admin.sharepoint.com) with your tenant name and with the site URL, such as https://example.sharepoint.com/sites/sample. Note that your site URL and the tenant URL are not the same.
   1. Connect-SPOService -Url "https://[your tenant]-admin.sharepoint.com"
   2. Set-SPOSite -Identity https://[your tenant name].sharepoint.com</sites/sample> -DenyAddAndCustomizePages $false

NOTE: the Set-SPOSite is to be per site colleciton, for example: https://example.sharepoint.com  and https://example.sharepoint.com/sites/sample  are 2 separate site collecitons. You may need to run this per site collection if you are editing more htan one site collection's infowise Clasic forms.

NOTE: this setting will remain for 24 hours, after which SharePoint will automatically reset them back to Deny. It is not possible to make this setting remain for longer than 24 hours. We suggest you ensure you are using version 1.4.0.0 and modern forms, which do not require this permission.