Essentials for Office 365 2.15 - Installation Guide

Migration of a Classic Experience Site to a Classic Experience Site with a 401: Unauthorized error

Issue

When performing a SharePoint Online to SharePoint Online migration, the following error is logged for Classic Experience site pages:

The server sent HTTP status code 401: Unauthorized

Possible Reason

The "Allow access" option is not enabled for apps that do not use modern authentication.

Resolution

1.Open the SharePoint admin center.

2.Navigate to Policies > Access control.

3.Click Apps that don't use modern authentication and set it to Allow access.