If data.json is only on your PC and not committed to your git repo, it won't exist on railway. Check if it's in your .gitignore .. if so,it's not being deployed. You'd need to git add data.json and push...Also If your app creates data.json at runtime, it gets wiped on every redeploy(ephemeral). To persist files, attach a volume to your service (click your service -> Add Volume, mount at e.g. /data) and update your app to write to /data/data.json.then to see the file you can SSH in using railway ssh and check your working directory.

I need the data that app creates at runtime, There is no option to add a volume, it's bcoz I'm currently trial user??

 Volumes should be available on trial version as well.. you get up to 0.5GB and 3 volumes. Right click your service ->select "Add Volume."