During my war against the Beotians, they had a civil war. I annexed Beotia and later made Beotian Rebels my client state. The client state was attacked by the Egyptians and I wanted to trade it away in a peace treaty after every province they owned were conquered. There were no peace options regarding them. I tried to annex them via console after the white peace with Egypt, didn’t work. Seems like it may be a bug.