next.js/examples/api-routes-apollo-server-and-client-auth/lib/form.ts

export function getErrorMessage(error) {
  if (error.graphQLErrors) {
    for (const graphQLError of error.graphQLErrors) {
      if (
        graphQLError.extensions &&
        graphQLError.extensions.code === "BAD_USER_INPUT"
      ) {
        return graphQLError.message;
      }
    }
  }
  return error.message;
}