Remove Specific Field matching pattern

Elastic Stack Logstash
2 
if  "[response][body][entries][values]" == '^n1D.*' { drop { }  }

This will not work because it is checking if the field value is exactly equal to that string, it is not a regexp match (which would be =~ instead of ==) and it is testing the field value, not the field name.

ruby {
    code => "
        event.to_hash.keys.each { |k|
            if k.start_with?('n1D')
                event.remove(k)
            end
        }
    "
}

This does not work because it only tests the top-level fields (e.g [response] in your example). If you just need to do this for that one field you could try

ruby {
    code => '
        v = event.get("[response][body][entries][values]")
        if v.is_a? Hash
            v.to_hash.keys.each { |k|
                if k.start_with?("n1D")
                    event.remove(k)
                end
            }
        end
   '
}

If you need to recursively process all fields of an event then see this thread.