Could you please share a screenshot of your flow's configuration?
The 403 FORBIDDEN error told that you don't have access to this SharePoint page. Please check if you have logged in your SharePoint with proper Office 365 account. Also please clear cache of your browser and retry again to check if the issue is solved.
In addition, please re-run your flow to duplicate a new SharePoint page and then check if issue still exists.
Community Support Team _ Kris Dai If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.