AppFlow SharePoint OAuth Error: AADSTS50011 with custom Azure AD app despite correct redirect URI

We’re running into the same problem: and as soon as we add https://3rdp.oauth.console.api.aws to Azure AD’s Redirect URI list—alongside the proper AppFlow URI—Microsoft bounces us straight to the screen below.

When setting up a custom Azure AD app registration for use with Amazon AppFlow's SharePoint connector, the redirect URI issue you're experiencing is a common problem.

The error message indicates that AppFlow is attempting to use a different redirect URI than the one you've configured. This happens because when you use your own app registration (instead of the AWS-managed client app), you need to ensure that you've added all the necessary redirect URLs to your Azure AD app registration.

For your custom app registration in Azure AD, you need to add the following redirect URI:

https://eu-central-1.console.aws.amazon.com/appflow/oauth

Make sure this exact URI is added to the list of redirect URIs in your app registration in the Microsoft Azure portal. The format must match precisely, including the region (eu-central-1 in your case).

Additionally, verify that:

1. You've properly registered your app in the Microsoft Azure portal
2. The app has the correct permissions (Sites.Read.All as you mentioned)
3. The client ID and client secret you're using in AppFlow match those from your Azure AD app registration
4. Your tenant ID is correct

If you've confirmed all these settings are correct and you're still experiencing the issue, you might need to clear your browser cache or try a different browser, as OAuth authentication can sometimes be affected by cached credentials.
Sources
Microsoft SharePoint Online connector for Amazon AppFlow - Amazon AppFlow
OAuthCredentials - AmazonAppFlow