I suspect this is as Lucas mentioned and you're not providing this as the body of the request. It's hard to tell without seeing each tab of your API setup. In your original video, you were applying the formula to a query parameter, which would be incorrect. You need to navigate to the 'Body' tab and apply the formula there, while also ensuring that it is formatted correctly. Looking at your screenshot, you still need to provide the messages as an array of objects and in this case your sending an object of objects that contain duplicate keys, which you can't do - each key has to be unique. If you need to send more than one object with the same key/value pairs, each object must go into an array.
@Lord Almighty
@Tom Ireland
@Lucas G
.jpeg/public)