Is the Istiftah Du'a (the opening supplication) recited in Tarawih prayer after every Takbir or once at the beginning of the first two Rak'ahs?

The opening supplication (Du'a al-Istiftah) is prescribed after every ihram (entering into prayer) except in the funeral prayer. It is also prescribed for a latecomer (masbuq) if he joins the Imam in a state other than standing (qiyam). If the Imam makes the tasleem after two rak'ahs and then enters into another prayer (with a new ihram), the opening supplication is prescribed for him. The Istiftah is recited only in the first rak'ah.