Error configuring Email provider on next-auth

Question

I am following the official documentation and also some online tutorial on how to configure email provider with next-auth, this is my config file:

export default NextAuth({
    adapter: MongoDBAdapter(clientPromise),
    providers: [
        GoogleProvider({
            clientId: process.env.GOOGLE_PROVIDER_CLIENT_ID,
            clientSecret: process.env.GOOGLE_PROVIDER_CLIENT_SECRET
        }),
        LinkedInProvider({
            clientId: process.env.LINKEDIN_PROVIDER_CLIENT_ID,
            clientSecret: process.env.LINKEDIN_PROVIDER_CLIENT_SECRET
        }),
        EmailProvider({
            server: {
                host: process.env.EMAIL_SERVER_HOST,
                port: process.env.EMAIL_SERVER_PORT,
                auth: {
                    user: process.env.EMAIL_SERVER_USER,
                    pass: process.env.EMAIL_SERVER_PASSWORD
                }
            },
            from: process.env.EMAIL_FROM,
            maxAge: 60 * 60 * 24 * 30
        })
    ],
    secret: process.env.NEXTAUTH_JWT_SECRET,
    theme: {
        colorScheme: "light"
    },
    pages: {
        signIn: "/signin",
        signOut: "/",
        newUser: "/"
    },
    callbacks: {
        async session({ session, token, user }) {
            session.user = {
                id: user.id,
                email: user.email,
                isAdmin: user.isAdmin,
                image: user.image
            };
            return session;
        }
    }
});

when I go to /signin I can see a page with 3 buttons: Google, linkedIn and Sign in with email. Google and LinkedIn work as expected. When I click on the 3rd one, I get redirected to

/signin?callbackUrl=http%3A%2F%2Flocalhost%3A3000%2Fsignin&error=EmailSignin

The examples I've seen so far shows I should use async jwt() in the callback, however this configuration has been working for months with the other 2 providers so I don't want to change it for the 3rd one, unless really necessary.

In place ot the 3rd button, I'd expect to see a form where to enter an email address.

Any idea how can I debug this?