Signing in to the organization's sign in page on iOS mobile devices using case-insensitive credentials results in "Error 400. Unable to generate token. details ["Invalid username or password."]." This causes users to be unable to log in unless using case-sensitive credentials; however, signing in to the ArcGIS Online home page at https://www.arcgis.com/home/signin.html on mobile devices does not require case-sensitive credentials, which creates inconsistency when logging in via mobile devices.
Since this bug was logged, the mobile site was redesigned and this is no longer a reproducible issue.
解决办法
Go to the ArcGIS Online home page located at <a href="https://www.arcgis.com/home/signin.html" target="_blank">https://www.arcgis.com/home/signin.html</a>, instead of the organization's sign in page, when using case-insensitive credentials on a mobile device.