Hello!

I have a backend node app on Railway, and the frontend is deployed to Vercel.
I'm trying to sync variables between both apps for the PR environments, but I'm unable to do so.
As you can see in the image, there's no preview environment, although I have it configured on Vercel.

The production environment works fine as the variables I need (In this case, the domain URL) are correctly synced.
Is there any guide or step I need to follow? Let me know in case you need more info!