Copying pages in OneNote not working

Your destination-section id matches the documented copyToSection request body, so I would first separate request failure from asynchronous copy failure. The action is available in Microsoft Graph v1.0; reproduce there rather than relying solely on the beta version you are currently testing.

In Graph Explorer, select v1.0, confirm that the signed-in account can access both the source page and destination section, and check the delegated permissions. Microsoft lists Notes.Create as the least-privileged delegated permission for this action.

A successful initial request returns 202 Accepted and an Operation-Location response header. Poll that operation until it completes; acceptance alone does not mean the page has been copied. If the initial request or operation fails, retain the HTTP status, error body, request ID, and timestamp for investigation. Your post does not include those results, so it cannot yet establish whether this is a permission issue, failed operation, or service regression.