Simplify the following text for a Grade 9 native English-speaking person.
Original: The Supreme Council of the IRB , which had been kept informed in detail about every facet of the Treaty negotiations and which had approved many of its provisions , voted unanimously to accept the Treaty , with the single notable exception of later COS of the IRA Liam Lynch .
Simplified: The Supreme Council of the IRB , which was informed in detail about the Treaty negotiations voted unanimously ( without exceptions ) to accept the Treaty . The only exception was the later COS of the IRA Liam Lynch .