Had confusing error exiting preview, with function by created with slicemachine init function.
If someone else ends up with it just add default to /api/exit-preview endpoint
Should look like that
import { NextApiRequest } from "next";
import { exitPreview } from "@prismicio/next";
import { NextApiResponseLike } from "node_modules/@prismicio/next/dist/types";
export default async function handler(req: NextApiRequest, res: NextApiResponseLike) {
return exitPreview({ req, res });
}