You are ready to design a form in SharePoint Designer, but you need to open your Office 365 SharePoint Site in Designer first.
You just use the URL!
- Open your O365 SharePoint Site in your web browser.
- Open Designer, and click Open Site.
- Copy the URL from your web browser to the Open Site dialog, ensuring you do NOT include the “default.aspx”.
- Your Site will open right up! Click Open.
Designer will spend a minute preparing everything and then you’ll be good to go!