Hi Pete, and welcome to the first step on your Postman journey
I’ll suggest some debug steps, but one thing to check first of all (because it catches me out all the time): check that you haven’t accidentally copied any extra whitespace or linebreaks when copying/pasting the URL into the address field. You should just about be able to make out this problem in the screenshots below - in the first one, the dot indicates an extra space at the end of the URL, and in the second one, the arrow indicates a linebreak/carriage return.
(As if to prove a point, I also accidentally put a space at the start of both of those URLs - I didn’t intend to! - which meant I was seeing strange results when writing this out for you)
I’ve confirmed that the typicode site will give a 404 in both of those situations, so hopefully it’s as straightforward as that!
If you need to debug further, if you look in the very bottom-left of the Postman interface you will see a “Console” link. This will be a lifesaver throughout your time with Postman; you can make messages appear here when debugging (by using console.log statements), but also whenever you press Send, it will automatically display an entry which contains the full details (headers/body information) about the request you made, and the response that you got.
If you paste a full dump of that in here, we should be able to get to the bottom of the mystery - as you say, this should be as straightforward as it gets, fingers crossed!
Example of request/response header information in console