If you have only received two doses of Pfizer and have not taken any previous vaccines (such as Sinopharm), you are most likely due a booster dose. Since the Green Pass was introduced, they gave a one-month grace period for Sinopharm recipients to get a booster. This grace period has now ended. Now as a minimum, you must have had your two doses of Pfizer + a booster after six months. If you go a day over that 6 months, your app instantly turns grey. If you had two doses of Sinopharm initially, then two doses of Pfizer, your app will remain green as long as you have regular negative PCR results at least every 14 days.