Hi,
NOTE: this article has been modified since its original version to align it with the current situation in SharePoint Online.
UPDATE: Starting with version 1.4.0, you no longer need this permission if you are only working with modern forms. Make sure to upgrade to the latest version as soon as possible.
Microsoft is now imposing a Deny permisson for Add and Customize pages in all sites. Which means that users cannot modify the site pages, and, as the result, Ultimate Forms cannot modify forms either when publishing classic forms or Modern forms in versions earlier than 1.4.0.
As a temporary measure, you can execute the following script to disable the permission rule. Note that is will be automatically restored after 24 hours. There is no way to remove the permission rule for good.
- If you haven't done so, install SharePoint Online Management Shell
- Run the following commands, replace <tenant> (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 <url> 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.
- Connect-SPOService -Url "https://<tenant>-admin.sharepoint.com"
- Set-SPOSite -Identity <url> -DenyAddAndCustomizePages $false
Schedule upgrade to version 1.4.0 and switch to using Modern form to avoiding running into this issue.