§ 71a AsylG means that you have already been applied for asylum in another safe third country (Sicherer Drittstaat). This was rejected there. Now you have submitted a new application in Germany. This is then referred to as a "Zweitantrag". Without knowing what's in the letter, I can't say much. However, it may be that the Bamf rejected your asylum application ... To say more, I would have to know what was in the letter from the Bamf.