Mongodb not limiting output when using limit in the pipeline

Question

      final pipeline = AggregationPipelineBuilder()
      .addStage(Match(where
          .eq('_id', ObjectId.fromHexString(authDetails.subject))
          .map['\$query']))
      .addStage(Match(
          where.eq('messages.username', theirUsername).map['\$query']))
      .addStage(Project({
        '_id': 0, //You can use as:'customer' instead of this keyword.
        'messages': Filter(input: '\$messages', cond: {
          '\$eq': ['\$\$this.username', theirUsername]
        }).build(),
      }))
      .build();

No matter where I add limit(5) I get back the same results. I've tried asking a few people but nobody seems to know how to fix it, But, trying on here, hopefully someone knows mongodb enough in dart to suggest a solution