Compound data array subdocuments with other array of subdocuments

[
  {
    '$match': {
      'Version': 18, 
      'ClientNavision': '51', 
      'Clients.Id': '1', 
      'Clients.Active': true
    }
  }, {
    '$lookup': {
      'from': 'Customers', 
      'localField': 'Clients.Fields.Id', 
      'foreignField': 'Fields.Id', 
      'let': {
        'domains': '$Domains', 
        'client_fields_id': '$Clients.Fields.Id', 
        'client_fields_value': '$Clients.Fields.Value'
      }, 
      'pipeline': [
        {
          '$match': {
            '$expr': {
              '$eq': [
                '$Fields.Id', '$$client_fields_id'
              ]
            }
          }
        }, {
          '$project': {
            'Fields': 1, 
            'Domains': 1, 
            '_id': 1
          }
        }
      ], 
      'as': 'fields_complete'
    }
  }, {
    '$project': {
      '_id': 0, 
      'ClientNavision': 1, 
      'Site': 1, 
      'Relations': 1, 
      'Fields': 1, 
      'Clients.Fields': 1, 
      'Clients.Id': 1, 
      'Clients.Active': 1, 
      'Clients.Local': 1, 
      'Clients.Cp': 1, 
      'Clients.ClientI18': 1, 
      'Clients.ContactPhone': 1, 
      'Clients.ClientName': 1, 
      'Clients.Direction': 1, 
      'fields_complete': 1
    }
  }, {
    '$unwind': {
      'path': '$Clients', 
      'preserveNullAndEmptyArrays': true
    }
  }, {
    '$match': {
      'Clients.Id': '1', 
      'Clients.Active': true
    }
  }, {
    '$unwind': {
      'path': '$Clients.Fields', 
      'preserveNullAndEmptyArrays': true
    }
  }, {
    '$project': {
      'ClientNavisionId': '$ClientNavision', 
      'Site': '$Site', 
      'Relations': '$Relations', 
      'Value': '$Clients.Fields.Value', 
      'Id': '$Clients.Fields.Id', 
      'Description': '$Clients.Fields.Description', 
      'ParentId': '$Clients.Fields.ParentId', 
      'Type': '$Clients.Fields.Type', 
      'Size': '$Clients.Fields.Size', 
      'Default': '$Clients.Fields.Default', 
      'Order': '$Clients.Fields.Order', 
      'Members': '$Clients.Fields.Members', 
      'I18List': '$Clients.Fields.I18List', 
      'ClientId': '$Clients.Id', 
      'ClientI18': '$Clients.ClientI18', 
      'FieldsMatch': '$FieldsConnection', 
      'Stockdata': '$stockdata'
    }
  }, {
    '$sort': {
      'Created': 1
    }
  }, {
    '$limit': 100
  }
]