iOS required for Planner mobile app

What is the earliest iOS supported for Apple devices for the Planner app? On the https://support.office.com/en-us/article/microsoft-planner-for-ios-help-a251cd45-f48d-4e24-966a-2fd36cfa143e, but when I try to download the app on an iPhone 5 I get told that it requires iOS 11. Do you know which one is correct?

Error message when trying to download the Planner app.