Smartthings Installation

Hi, I am a newbie to Home Assistant and slowly getting all my existing home automation integrated.

Please can anyone help with getting Smartthings integrated. I seem to be going round in circles and after several hours no further forward. All the installation guidance out on the internet seems to be for an older configuration of Home Assistant so the usual internet searches haven’t been of much help.

I am trying to follow the instructions her SmartThings - Home Assistant

I know that and the port forwarding is all setup correctly as I have DuckDNS working as an external URL on my iPhone app.

I added the following to my config.yaml

homeassistant:
	external_url: "https://example.duckdns.org"

This seemed to get me past the first hurdle which at least allowed me to install the Smartthings integration. What I am now struggling with is getting the webhook recognised by Smartthings.
Not knowing where the webhook address is generated from I selected the default address presented in the configuration dialog. Unfortuately this is not recognised. Is this because I haven’t setup ‘Let’s Encrypt’ and hence SSL? If so how do I setup ‘Let’s Encrypt’ as its no longer an available integration?

Any assistance greatly appreciated.

Home Assistant 2024.3.0
Running as a Docker Installation on Linux