SSL Error - Alert number 80 - When calling server from client - node.js

Question

I am a newbie in web development, I developed my first basic CRUD app. It works as expected in my local. As a portfolio item, I wanted create an actual website. I bought domain name & SSL certificate etc, deployed my back end and front end etc. However I am struggling with an issue for the last couple of days. Please see the details below
Background Info
Server: I have a nodejs application on Heroku (example.com). I bought an ssl certificate for my domain (i.e. example.com). I inserted certificate and intermediate certificate in Heroku and linked with my back end.
Client: I deployed my React & nextjs frontend on Vercel (subdomain.example.com). Vercel is creating its own certificate for subdomain.example.com
My issue is that I am receiving the following error in my website. After I wait couple minutes and refresh the error disappears. If I don't use it for some time again, the error reappears.
[Network] FetchError: request to https://example.com/graphql failed, reason: write EPROTO 139801265354624:error:14094438:SSL routines:ssl3_read_bytes:tlsv1 alert internal error:../deps/openssl/openssl/ssl/record/rec_layer_s3.c:1544:SSL alert number 80
See below my code for nodejs
const conn = await createConnection({
type: "postgres",
url: process.env.DATABASE_URL,
host: process.env.PG_HOST,
username: process.env.PG_USER,
password: process.env.PG_PASSWORD,
port: parseInt(process.env.PORT),
database: process.env.PG_DATABASE,
logging: true,
migrations: [path.join(__dirname, "./migrations/*")],
entities: [Bank, User, Report],
ssl: __prod__ ? {rejectUnauthorized: false} : false
})
const redisStore = connectRedis(session);
const redis = new Redis(process.env.REDIS_URL);
app.set("trust proxy", 1)
app.use(cors({
origin: __prod__ ? process.env.CORS_ORIGIN : "http://localhost:3000",
credentials: true
}))
app.use(
session({
name: COOKIE_NAME,
store: new redisStore({
client: redis,
disableTouch: true
}),
cookie: {
maxAge: 1000 * 60 * 60 * 24 * 365 * 10,
httpOnly: true,
sameSite: "none",
secure: __prod__,
domain: __prod__ ? process.env.DOMAIN : undefined
} as CookieOptions ,
saveUninitialized: false,
secret: process.env.SESSION_SECRET,
resave: false
})
)
const apolloServer = new ApolloServer({
schema: await buildSchema({
resolvers: [BankResolver, UserResolver, ReportResolver],
validate: false
}),
context: ({req, res}): MyContext => ({req, res, redis})
})
await apolloServer.start()
apolloServer.applyMiddleware({app, cors: false});
app.listen(parseInt(process.env.PORT), () => console.log("Server listening on port 4000"));
}