Hey, you can set a limit by clicking on "limit", I have attached a screenshot below.

Don't have that, does my plan not support limits?

Oh, I see that you have the credit based hobby plan. I believe that it is indeed not possible to set a limit on a credit based plan.

So if I use all my credits I am not billed anything, my projects just stop till I buy more credits?
I guess this is related to my plan, so I if use my credits I need to sub to a different plan

"What happens if I use credits as a payment method and my account runs out of credits?

If you are using credits as a payment method and your credit balance reaches zero, your subscription will be cancelled. You will no longer be able to deploy to Railway and we will stop all of your workloads. To resolve this, you will need to sign up for a new subscription after topping up sufficient credits."

As per the docs, this is indeed correct.