Hello Joel, the Raspberry Pi is required to establish the MQTT connection between your devices, because it runs Mosquitto MQTT broker.

Yes, you can also use a free CloudMQTT broker as I show in this thread: https://rntlab.com/question/using-cloudmqtt/

CloudMQTT is free for a couple of devices, after that it’s a paid service that’s I prefer to run my own MQTT Broker.