20:9 Shemoneh Esrei is not repeated unless there are at least six men, which is the majority of a minyan, who have just recited the individual Shemoneh Esrei. If there are not six, Shemoneh Esrei is not repeated. Rather, one person should recite Shemoneh Esrei through the blessing of “HaKeil haKadosh,” after which Kedusha is said, then everyone says the silent Shemoneh Esrei.

20:10 There are errors that, if made, would require a person to repeat Shemoneh Esrei. The same parameters apply to a shaliach tzibbur in regards to the public recitation of Shemoneh Esrei; if he makes such errors, he must repeat the public Shemoneh Esrei. The sole exception is that if the shaliach tzibbur forgot to say “ya’aleh v’yavo” during shacharis on Rosh Chodesh or chol hamoed and he did not remember until he already completed his prayers, we do not make him repeat Shemoneh Esrei because doing so would inconvenience the congregation. In this case, we can rely upon him recounting the theme of the day in musaf and avoid him having to repeat. However, if he remembered “ya’aleh v’yavo” before finishing Shemoneh Esrei, he returns to “R’tzei” and this is not considered unduly inconveniencing the congregation. (Rema OC 126:3 and Mishna Brurah 126:14 tell us that the same applies if the shaliach tzibbur accidentally says the weekday Shemoneh Esrei during shacharis on Shabbos or Yom Tov.)