Hub Site association approval request fails with 403 Forbidden (previously working, regression)

Sites configured to require approval before joining our Hub Site are failing the association request with an HTTP 403 Forbidden error[browser DevTools Network tab}. This same workflow was functioning correctly as of [early August 2026]. Hub sites that do not require join approval continue to associate successfully — the failure is isolated specifically to the approval-required path.

Steps to Reproduce

1. As a site owner, go to Site Settings → Site Information (or Site Contents → hub association) on a site that is not yet associated with the hub.
2. Attempt to associate it with [Hub Site URL], which has RequiresJoinApproval set to $true.
3. Observe that the request fails immediately (or fails when the approver attempts to approve it — specify which point in the workflow fails).
4. Repeat the same steps against a hub site that does not require approval — association succeeds without error.

Expected Behavior
The association request should be submitted and routed to the configured approver(s) for review, consistent with behavior observed as recently.

Actual Behavior
Request fails with HTTP 403 Forbidden. [browser DevTools Network tab - attached the HAR file for reference]

Error Details

• HTTP Status: 403 Forbidden [browser DevTools Network tab - JoinHubSite(@v1)?@v1]

   

Troubleshooting Already Performed

• Confirmed association without approval works (isolates the issue to the approval workflow specifically)