I also tried setting RAILPACK_NODE_VERSION="22", but the error didn’t change... =/

Do you have a node version specified in your package.json?

Something somewhere is overwriting your node version because the default is node 22 on Railpack

My package.json doesn't specify any Node.js version.

And you're 100% sure you're using Railpack, you don't have a Dockerfile or anything?

I'm definitely using Railpack, and there's no Dockerfile in the project.

Railpack defaults to Node v22.

Can you send a link to the repository?

I can't, the project is private =(

Well. We can do this the hard way.

Can you send any Node or Yarn config files that are present?

Sure, attached.

Don't see anything in there. Any other files that might be?

There’s no config file that could be causing this… =(

I’m not sure what other file I could send you to check. =(

I can pretty much say that there's only issue with what version of node has been picked.

Railpack currently picks node v22 by default as loudbook said upper.
So it has to be fine even without RAILPACK_NODE_VERSION provided in Variables. But im recommend to keep this variable in case you changed node version earlier in the project.

Can you show that upper text in "Build Logs" (as on my screenshot) so we can make sure that it picked correct node version? If it differs - maybe that's is the problem.

I can confirm. With node v22 my empty project with your package.json and "yarn build" set as custom build command it was built fine.

Wow,
Thank you so, so much, everyone!

With your help and tips, I was able to find the problem, and it really was in my project's configuration.

I found the .nvmrc file, and it had version 20.11 — I changed it to 22, and that solved the issue. =)

Thank you so, so much, everyone.

Grateful!!