Stoning the Devil is an obligatory duty of pilgrimage.
“Remember Allah during that specific days. Whoever hastens in two days, there is no sin upon him; and whoever delays, there is no sin upon him so long as he guards himself. (…)” (Al-Baqarah/ The Cow 2:203)
The verses before this one mention the duty of pilgrimage. When we read this verse we understand that: to hasten to or from somewhere, a person should be out of his home, at some specific place.
Narrated Abu Huraira: The Messenger of Allah said, “Whoever performs Hajj for pleasing Allah, and does not have sexual relations with his wife, and does not do any sins; he will return as if he were born anew.” (Bukhari, Hajj/Pilgrimage, 4)
This narration is in accordance with the verse above. Whoever hastens in two days will return without sins, and whoever stays one more day would also return without sins, as long as he/she guards the self from sins.
There should be a specific place to hasten to or from. That means, there is a place in order to remember Allah during those two or three days, and those days are the specific ones during pilgrimage.
The duty of pilgrimage is an obligatory duty since Prophet Abraham. Prophet Muhammad also performed it. There are many verses that mention Hajj.
“Take places of prayer from the standing places of Abraham.“ (Al-Baqarah/ The Cow 2:125)
These standing places are the places that Abraham stood for Hajj. One of those places is Mina, where he stoned the Devil.
We name the Devil as “Rajeem” which means “stoned”. Whenever people perform the duty of Hajj, they should also go to Mina and stone the Devil in order to be one of those who stone it.
When we read these verses and narrations together, it becomes clear that stoning of the Devil is of obligatory duties in Hajj and should be performed during those specific days. The word ‘maqam’ has no plural form. It is assigned singular or plural meaning according to the sentence it is mentioned in. Since the people that perform pilgrimage (Hajj) or Umrah pray at more than one place, we assign plural meaning to the word.  These places are Arafat, Muzdalifah, Mina, Safa, Marwa, Mina, Kabah and its vicinity.