Subscribed Notifications Not Working

Hi all, I'm trying to move my important apps from ST to Hubitat and I'm working on a garage door notifier app on a raspberry pi. I think it's 99% working.

This is the version I'm working with (the only change from the original author's is that I've replaced physicalgraph with hubitat for LAN interaction.) The App imports, discovers my garage doors, and creates the virtual device. If I use the poll button it will get and display the correct open/close state.

However, the device subscribes to events and when the state changes the app sends a notify to HE. I can see the HTTP POST being sent but I don't think it is making it to the app. I don't see anything in the HE logs when the notify sent (nothing at all.) I sniffed the exchange and hubitat is responding with "Bad Message 400 reason: Duplicate Content-Length"

Other items I've checked from reviewing other threads here include my Device IDs being the correct MAC address of the device in hex form, upper case, no separators. I see HE refresh its subcription to events regularly and the notify is being sent on port 39501 as expected.

Can someone please take a look at this? It's a great app I'd love to see working with HE. The raspberry pi side of this is in the repo too.

Thanks!

I was able to send a successful notify using curl which led me to capture and compare the differences. The Content-Length header was indeed being set twice. I guess ST ignored that, HE doesn't like it. Removed the extra and I can get notifications.