Translation:I no longer know what you said half a year ago.
why not past perfect here?
Because the past perfect is used when the main verb is in the past and the event you are referring to happened further back in the past. So it would be "Ik wist niet meer wat je een half jaar geleden had gezegd".
Was marked wrong for "I don't know what you said a half year ago anymore". Anything incorrect with my translation?