When Hadadezer’s subjects saw that they had been defeated by Israel, they made peace with David and became subject to him. So the Arameans were unwilling to help the Ammonites anymore.
Jewish Publication Society of America Version (JPS1917) - 1 Chronicles 19:19 >And when the servants of Hadarezer saw that they were put to the worse before Israel, they made peace with David, and served him; neither would the Arameans help the children of Ammon any more.