Yahoo mail in iOS mail problem FIXED finally.

My Yahoo Mail app and Yahoo online worked fine, but yahoo Mail in IOS mail gave various error messages. I have finally fixed the problem. In settings, go to app, mail accounts & choose Yahoo, account settings, go to advanced settings. Under Incoming Mail Settings in IMAP Path Prefix if the \ is greyed out enter\. Save, if required. Exit. Reboot iPhone or iPad. If there are no subfolders in your Yahoo account enter INBOX instead of \. I hope this helps others with the same problem. It worked for me.