What is the niyat of qaza e umri. It's wajib or not?

If it’s done in place of ones lapsed wajib namaz, then niyyat would be wajib and should be prayed same as wajib by which I mean 2 raka’at of Fajr should be 2 Raka’at and Maghrib 3 and Isha and Zohr and ASR will be 4. And if you are praying 2-2 raka’at just as a mustahab, then it’s niyyat will be sunnat Qurbatan Ilallah.