InvalidCheck: pkceCodeVerifier value could not be parsed. Read more at https://errors.authjs.dev#invalidcheck

Question

I am trying to set up next-auth using a tutorial for authjs v5. I am getting this InvalidCheck error on Vercel: InvalidCheck: pkceCodeVerifier value could not be parsed. Read more at https://errors.authjs.dev#invalidcheck while trying to sign up with Google for the very first time.

I am directed to the sign in page for Google, and the Oauth process seems to complete, before landing on the error page.

This results in a 504 error This Serverless Function has timed out. Which then requires me to clear the storage and cookies before trying again.

I am using NextJS 15.

My code works perfectly on localhost though.

Here is my auth.ts:

  import NextAuth from "next-auth"
  import Google from "next-auth/providers/google"
  import client from "@lib/db"
  import User from "@models/user"
  import { connectToDB } from "@utils/database"
  
  export const { handlers, signIn, signOut, auth } = NextAuth({
    providers: [Google],
    callbacks:{
      
      async session({session}){
        const sessionUser = await User.findOne({  email: session.user.email })
        // console.log("sessionUser", session)
        if(sessionUser){
          session.user.id = sessionUser.id
        }
        return session;
      },
      async signIn({ account, profile, user, credentials }) {
        try {
          await connectToDB();

          // check if user already exists
          const userExists = await User.findOne({ email: profile.email });

          // if not, create a new document and save user in MongoDB
          if (!userExists) {
            await User.create({
              email: profile.email,
              username: profile.name.replace(" ", "").toLowerCase(),
              image: profile.picture,
            });
          }

          return true
        } catch (error) {
          console.log("Error checking if user exists: ", error.message);
          return false
        }
      },
    }
  })

I've tried to follow steps for the PKCE code_verifier cookie was missing on upgrade error. However, this did not seem to resolve my issue. Any help would be greatly appreicated.