Home-assistant.io/integrations/smartthings/#troubleshooting

I’m trying to debug my SmartThings Integration.
Under bullet #4 in the SmartThings - Home Assistant there is a suggested curl command to test the webhook integration. When I execute this curl command, I get the following respons:

curl: (6) Could not resolve host: PING,
curl: (3) URL using bad/illegal format or missing URL
curl: (6) Could not resolve host: 00000000-0000-0000-0000-000000000000,
curl: (3) URL using bad/illegal format or missing URL
curl: (6) Could not resolve host: en,
curl: (3) URL using bad/illegal format or missing URL
curl: (6) Could not resolve host: 1.0.0,
curl: (3) URL using bad/illegal format or missing URL
curl: (3) unmatched brace in URL position 1:

I’m not a curl expert, but surely ping cannot DNS resolve an address on using https (or http) format ?
But I tried without the http(s) and the result is the same.
If I ping directly, it works well so there’s no problems with ping reply. My public URL is on the form: ha.mydomain.com and it uses Let’s Encrypt SSL and passes through a Reverse Proxy. Perhaps that’s causing issues?