Is the admonition given by the Imam between the fourth and fifth oaths a required element of Li'an?

Primary text

The admonition given by the Imam to both parties after the fourth utterance and before the fifth is recommended according to the majority of scholars. This is supported by the narration of Ibn Abbas regarding Hilal, who was warned during the fifth oath that it was the statement that would necessitate punishment, and he proceeded, stating he would not be punished after not being flogged. Similarly, the wife was warned, hesitated, and then affirmed her oath.