Open Integromat App (Zapier Alternative)

I once used Zapier for a lot of automation things but I now find Integromat better in both price and capability.

I could use the Join API to manage device queries and messages easily enough. In fact, I have successfully queried for devices from Integromat. However, this method means I need to input my authentication (API key) and device (Device ID) details in each scenario that I create.

Instead I'd like to create a Join "app" within Integromat that allows me to persist my API key and will make it more streamlined to select devices when creating messages/notifications. Integromat allows me to create the connections and functions easily enough but completing the JSON is a bit technical in nature.

As you can see in Integromat, there are lots of options and if anyone has created Join as an "App" in Integromat before, I'd greatly appreciate your help setting these up.