when I try to add new items to an array inside a document I get this error. As far as I know, the item references do exist in the MongoDB database.

The error i get is:

[
  "To resolve this issue please update or replace the document in MongoDB to make sure it abides by the schema.",
  "Change Event Type: update",
  "Namespace: app.CompanyLocation",
  "Partition: dag1f7g7102aecdd3e9467711e",
  "Document ID: ObjectID(\"61f7f74a2aecdd3e9467711f\")",
  "Detailed Error: cannot insert link at index 7 of array at path { table: \"CompanyLocation\", fullPath: \"units\" }, array has 6 elements and backfilling nulls in array of links are not supported",
  "Number of Unsyncable Documents: 1"
]

The code causing the error is:

 const newUnits = result.Shipment.Units[0].Unit.map(u => u._attributes.UID +  u._attributes.PSN).flat();
  console.log(newUnits);
  if(importResult.success){
  // Lägg till den som inventory på platsen.
  context.services.get("mongodb-atlas")
  .db("app")
  .collection("CompanyLocation")
  .updateOne(
    {
      _id: new BSON.ObjectId(place), 
      _partition: partition}, 
      {
        $push: {
          units: {
            $each: newUnits
          }
          
        }
        
      }
    )
  console.log(newUnits);
}

My question is: What may be causing this & What does the error message mean?