WWW::Efa::Error::Backend - WWW::Efa unknown error from efa.vrr.de

    use WWW::Efa::Error::Backend;

    my $error = WWW::Efa::Error::Backend->new(
        'Yadda Yadda'
    );

    die $error->as_string();
    # WWW::Efa error from efa.vrr.de:
    # Yadda Yadda

Received an unknown error from efa.vrr.de

Return the error as string, can directly be displayed to the user