A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hi Mike,
To open SharePoint Site in SharePoint Designer 2013, you can try the steps below:
First, you need to enable Custom Script in SharePoint online Admin center.
Go to SharePoint online Admin center>Settings>Custom Script>check Allow users to run custom script on personal sites and Allow users to run custom script on self-service created sites like below>select OK on the bottom.
Note: changes will take 24 hours to take effect.
Then perform the steps below:
1.Open the SharePoint online site in web browser.
2.Open SharePoint Designer>Open Site
3.Type the URL of SharePoint online site(for example: https://yourtenant.sharepoint.com) in the Site name box
4.If you get the no permission error, please wait as the custom script change takes 24 to take effect.
Regards,
Tina
[Updated by Tina Chen MSFT, June 14th, 2:17PM (UTC)]