Where can I see my purchases
I cannot sign in to Microsoft on either device.
iPad Pro 12.9-inch, 3rd Gen, Wi-Fi, Cell
So what is your actual question?
To see your purchases click here and follow the instructions -> See your purchase history for the App Store, iTunes Store, and more - Apple Support
For your other question, you will need to provide details about the issue. Are you trying to sign in in an App, on a website, for email? What happens when you try?