When I go to Marketplace and select an aircraft that I want to buy, I get a message that I need to use the same Microsoft login as when I bought the sim. When I load and login at Microsoft all works but sim still locks me out. Suggestions please?

Try purchasing your AC directly from the developer if possible. If you have a Xbox login try using that. My Microsoft store and Xbox are tied together as one. So, when I had no choice but to purchase from the MS store, I use the same login info or MS store knows it already and allow the transaction to go through.

Hope this helps.