It looks like your application can’t read the environment variable properly.
I don’t know which package you are using to load environment variables but the simplest way is using dotenv package.
After installing it with npm i dotenv, import it as early as possible in your application main file like this:
require("dotenv").config();
Create .env file in your application root folder with this content ( as you see the format is key=value)
MYSQL=jllgshllWEUJHGHYJkjsfjds90
JWT_KEY=secret
Then you can access their values like you already did:
process.env.JWT_KEY
.env file:
