explain redirect back error, when it comes
Rails API (api.rubyonrails.org) for redirect_to says:
When using redirect_to :back, if there is no referrer, RedirectBackError will be raised. You may specify some fallback behavior for this case by rescueing RedirectBackError.
The Referer header is usually sent with a request by a browser if the user goes to the page by clicking a link, and it contains the url of the page with that link. There is no Referer header if the user just types the address in the address bar, for example.
Yours sincerely, Damian/Three-eyed Fish