"Napa" Office 365 Developer tools have been fully retired on March 31, 2017.
Office and SharePoint add-ins remain a key avenue for connecting your applications to where users get work done within Office 365. To keep building Office and SharePoint add-ins, we recommend you take advantage of the built-in Office and SharePoint development workload within Visual Studio or use the free Visual Studio Code tools in conjunction with the Yeoman Office generator templates.
We will retain your generated add-ins till June 30, 2017, 90 days past the retirement date. Should you need access to your add-in data post March 31st, please contact us at NapaCloudAppTeam@microsoft.com.
The “Napa” team