Especially in front of Shangguan Xiu, he needs to appear more composed.
Moreover, in the recording he made, Chen Menglu admits with her own mouth that she killed her grandfather.
With such evidence, the truth about who the real murderer is becomes obvious.
Shangguan Xiu definitely needs this recording.
Then, he has to exchange it for the antidote.
Actually, thinking carefully, Ouyang Zhi feels a bit at a disadvantage in this deal with Shangguan Xiu, after all, he provided the evidence to save Shangguan Xiu's grandfather, but Shangguan Xiu merely gave him the antidote, which was meant for Jia Sen and has nothing to do with him.
However, thinking further, Jia Sen ended up plotting against the Shangguan Family because of his words and got poisoned, so there's really no need to fuss about it.
Shangguan Xiu heard Ouyang Zhi say he had a recording of the call with Chen Menglu, and it was made after the Old King was killed, when Chen Menglu, frightened, called Ouyang Zhi.
