How can I create a custom redirect page in SharePoint Online for broken links or access issues?

1. Create a Custom “Help / Error” Page

First, build the page you want users to land on:

Go to your Site Pages library.
Create a new modern page, e.g., /sites/Portal/SitePages/AccessHelp.aspx.
Include:
Explanation of common causes (permissions, cache, broken link)
Instructions to fix (e.g., “Press Ctrl+F5 to refresh”)
A button to go back to the Home Page
Contact IT/Support link or form (can link to a Microsoft Form or email)

Tip: Give it a friendly title like “Having trouble opening this page?”

 2. Handle “Broken Link” Redirects (404-style)

For broken or outdated URLs:

Option A – Site Redirect Rules (Native)

If the missing links are known or predictable:

Go to Site Settings → Navigation → Search and Offline Availability (classic admin center).
Use Redirects via site redirection mapping — available if your site uses the Publishing Feature (classic experience).
Example: redirect /oldpage.aspx → /SitePages/AccessHelp.aspx.

 Limitation: This works only for specific URLs, not a generic catch-all.

Option B – Redirect via Azure Front Door or CDN (Advanced)

If your SharePoint is fronted by an Azure Front Door or Reverse Proxy, you can configure a rewrite/redirect rule:

Match 404 responses → redirect to /SitePages/AccessHelp.aspx.
This requires admin control outside SharePoint (via Azure).

This approach gives full control but is only viable for larger organizations or intranets using custom domains.