Just after upgrading the c# driver to 2.5, my logic where I am using watch method to check for any updates on collection started failing with an error message.

GetRequestChanges method failed with error : Command aggregate failed: Unrecognized pipeline stage name: '$changeStream'

below is the code: and last line is where code breaks.
{{var db = ConnectMongoDB();
var options = new ChangeStreamOptions

;
var pipeline = new EmptyPipelineDefinition<ChangeStreamDocument<BsonDocument>>().Match(Builders<ChangeStreamDocument<BsonDocument>>.Filter.Empty);
var col = db.GetCollection<BsonDocument>("tblRequest");
var cursor = col.Watch(pipeline, options);}}

In documentation, I do see the very first point says

The 2.5.0 driver adds support for many of the new features introduced by the 3.6.0 server.

Change streams
The 2.5.0 driver adds support for change streams. See the Watch and WatchAsync methods in IMongoCollection.

but here I don't see anything that suggests any changes.

Can you suggest what's wrong here?