I tryed starting up the game again and it still doesn't appear is it just being delayed on my end or is it a bug ps4 slim.
I've always found the in-game store to be flaky at best. I normally either buy from the PSN app or from a web browser and then use the download queue to send it to my system. Simplest to visit https://store.playstation.com/en-gb/product/EP2866-PPSA03943_00-TRAINSIMWORLDPS5/ and click on the add-ons section.
This is weird, the in-game store is showing everything except the 313. The PSN app does not show the 313 either, and everything else, except the stuff l've purchased before the 313 was released, is marked as "Unavailable". The 313 is available using a browser but trying to buy it results in a "Something went wrong" error, and clicking on "Details" just returns the same message. I've always purchased through the in-game store and this is the first time I have had any problems.
The 313 shows up under the PS5 version of the game but is marked PS5 PS4. It doesn't show under the PS4 add-ons and it's the same for quite a few others now.