Teams is your encoder when using Teams to create the live event. Stream doens't have a built in encoder so you have to use one. Here are some supported known working ones you can choose from. I use OBS, but there are others as well. Takes some practice but it's not too difficult once you get the URL format right to stream to.
its the URL you get on the stream window when you launch it. in obs you pick custom, then the URL for server without the random number key at the end of the URL, put that into stream key. if that don't work put whole URL in server and the random key in the URL in stream key, it's been too long but that's all there is too it. Also make sure you click start stream.