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I'm testing my MAS app using Sandbox Test accounts - when I start the app I get the sign-in dialogue with the Apple ID field filled in with a previous account, and ready for password entry. However I want to change the Apple ID to use a different account but it won't open that field to edit.I'm sure this has been possible in the past - but now it is just frustrating - there doesn't seem to be a way to escape out of the pre-populated Apple ID.