So, I recently realized I may have been doing my dua incorrectly. I just read that the dua that you make before the tasleem is supposed to be from the Quran and Sunnah and I was just making my own dua, while my own personal dua should have been made after the tasleem. Does what I have done invalidate my salah? Can someone confirm what I read is true and if so, correct me in the act of dua and recommend a few short dua that I should do before tasleem?