$lookup - allowDiskUse

I m running a $lookup query . Source Collection is around 4 million rows. Joined collection is 8 millions

db.MediaPlans.aggregate([{$lookup: {
 from: 'AllPlacements',
 let : {
    mediaPlanDay : "$MediaPlanDay",
    placementID : "$PlacementID"
},
pipeline : [
  {
    $match : {
      $expr : {
        $and :  [
           {
             $eq :  ["$PlacementDay","$$mediaPlanDay"]
           },
           {$eq : ["$ExternalPlacementId","$$placementID"]}
          ]
      }
    }
  }
],
as: 'placements'
}, 
{
$unwind : {path :"$placements"}
}}, {$out: 'CollectionToSave'}],
{
	allowDiskUse: true
} )

I m getting that $lookup stage exceeded 100mb limit message

any idea why allowDiskUse is not working ?

@Abdourahamane_43688

This does not appear to be related to any work in this course. If this is a general question, I would strongly suggest that you post this on Stack Overflow or one of the MongoDB forums. This is not an appropriate Forum for general questions. Thanks.