please read this docs page for create-react-app https://create-react-app.dev/docs/adding-custom-environment-variables/

tl;dr variables on the frontend service must begin with REACT_APP_

I understand, I was already following these guidelines mainly regarding the REACTAPP prefix, even so it still seems that it is not recognizing the environment variable created in the variables session, to access the variables created in railway the code still uses process.env.REACTAPP .. . ?

correct, but make sure to read the docs page I linked.

Same happens to me, any solution??

Please read the docs page I linked in the first message.

As the previous mate told you, we have followed the instructions in the document and the problem persists. If you do not know the solution, no problem, but do not refer us to a document which several people have read and it has not solved their problem

Dockerfile or Nixpacks?

Dockerfile

Please read this docs section - https://docs.railway.app/guides/dockerfiles#using-variables-at-build-time

This finally resolved!!

You need to add 2 lines to the dockerfile to create the env variables on the right moment.

Using Variables at Build Time

If you need to use the environment variables that Railway injects at build time, which include variables that you define and Railway-provided variables, you must specify them in the Dockerfile using the ARG command.

For example:

# Specify the variable you need
ARG RAILWAY_SERVICE_NAME
# Use the varible
RUN echo $RAILWAY_SERVICE_NAME

Be sure to declare your environment variables in the stage they are required in:

FROM node

ARG RAILWAY_ENVIRONMENT

Yep that's what the docs say!