The add-in fails to connect to a specific list or library in SharePoint Online.
There are many reasons why this could fail. Please try out the following steps that will help you find your cause.
Resolution 1 | No access to the SharePoint Root Site
For any officeatwork 365 add-in to be able to connect to SharePoint in your Office 365 tenant each user that wants to connect needs at least read rights for your root site. Here are some step-by-step instructions on how you can check who has access to your root site in SharePoint.
click on the SharePoint icon on our Office 365 home page (office.com)
Change the URL in your Browser by removing everything that comes after sharepoint.com/ and then reload the page.
Click on the gear icon and choose ‘Site settings’
Click on ‘Site Permissions’
Check to see if all the users that need to work with SharePoint data are in one of the groups and have at least ‘read’ permissions.