Have you added something lke this in the pages > api > auth > [[...path]].js file:

// Next.js API route support: https://nextjs.org/docs/api-routes/introduction
import { superTokensNextWrapper } from "supertokens-node/nextjs";
import { middleware } from "supertokens-node";

export default async function superTokens(req, res) {
  return await superTokensNextWrapper(
    async (next) => {
      await middleware()(req, res, next);
    },
    req,
    res
  );
}