I see when I use Seller Dashboard max token lifetime is 3 year.
Does anybody know it how long it be valid if I use AppRegnew.aspx page?
I have found answer on official MSDN documentation How to: Replace an expiring client secret in an app for SharePoint
Client secrets for apps for SharePoint that are registered using the AppRegNew.aspx page expire after one year. This article explains how to add a new secret for the app.