Invocations for breaking the fast may be the following:
Dhahaba al-thama’ wa abtalat al-‘urooq wa thabata al-ajr insha’Allah
The thirst is gone, the veins are moistened and the reward is confirmed, if Allah wills.
Reference: Abu Dawud 2/306 and others. See also Al- Albani, Sahihul-Jami’ As-Saghir 4/209.
Allaahumma ‘innee ‘as’aluka birahmatikal-latee wasi’at kulla shay’in ‘an taghfira lee
O Allah, I ask You by Your mercy, which encompasses all things, that You forgive me.
Reference: Ibn Majah 1/557 from a supplication of Abdullah bin ‘Amr. Al-Hafidh graded it as good in his checking of An-Nawawi’s Kitabul-‘Athkdr. See Sharhul- Athkar 4/342.