Hi Tom, If I understand correctly your Device to Application (Means IoT Central Application), if Yes, then below info will help.
Please see the Build the IoT Central device bridge to connect other IoT clouds to IoT Central.
"The function app is the critical piece of the device bridge. It receives HTTP POST requests from other IoT platforms or any custom platforms via a simple webhook integration. You can easily extend this solution to connect to your custom IoT cloud if your platform can send HTTP POST requests to your function app. "
External systems can feed device data through this device bridge and into your IoT Central app by making HTTP POST requests to the function URL.
Get the IoT Central device bridge from GitHub.
Let us know if this helps your scenario.