I am trying to push my web application (MERN stack) to Heroku but I keep getting this error

enter image description here

What I have tried in index.js

if (!config.get("jwtPrivateKey")) {
throw new Error('FATAL ERROR!!: jwtPrivateKey is not defined')
}
console.log(config.get("DB"))
console.log(config.get("jwtPrivateKey"))

This is their value when i log them

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