I have done two posts on automating posting messages to teams.

The first is a general overview and the second is using Powershell.

In the course of posting a message via the HTTP end point, you should get a response as follows:

1

However there are times you may get this response

The resource you are looking for is unavailable

If you get this error, the problem is your end point.

Either you have a typo in the URL or you have not updated the channel URL.

How you check for the latter is by looking at the URL

If it starts with

https://office

Then it is out of date and you need to update it. Follow the instructions here to access the existing webhook. If it is out of date, there will be a button to update it.

Happy hacking!