Hi! Unfortunately it's not possible.

You can set hard limits in workspace settings so you don’t use more than a certain amount (eg, 100€).

But be aware that all deployments will be removed if you reach the limit.

-# I don't think that was the question he asked, he's asking if he can pre-pay 100€ in credits which is not possible since March 30th where Railway removed the pre-paid option

I know it’s not what he asked, but a possible workaround if op wishes to do so.

It doesn’t really answer the primary question but if your goal is to prevent costs above 100 euros, that’s one way to do it.