Failed to execute 'postMessage' on 'DOMWindow': The target origin provided ('<URL>') does not match

Topic summary

A Shopify app developer encountered a postMessage origin mismatch error causing all app pages to display blank screens. The console error indicated the target origin provided didn’t match the recipient window’s origin.

Root Cause & Resolution:

  • The issue was traced to the entry.server.tsx file
  • Developer had previously renamed it to entry.server.ts and modified its code while fixing another bug
  • Solution: Restored the original entry.server.tsx filename and reverted to standard code

Current Status:

  • Problem resolved after file restoration
  • Developer seeks clarification on what specifically went wrong and how entry.server.tsx functions

The error appears related to server-side rendering configuration in Remix/Shopify apps, where the .tsx extension and proper React server rendering setup are critical for correct origin handling during iframe communication.

Summarized with AI on November 13. AI used: claude-sonnet-4-5-20250929.

Failed to execute ‘postMessage’ on ‘DOMWindow’: The target origin provided (‘’) does not match the recipient window’s origin (‘’). in the console of my shopify app. which shows blank page on all the pages of my shopify app.

Can anyone give solution to my error, I have been stuck in this for two days.

Here is my code,

import { json } from "@remix-run/node";
import { Link, Outlet, useLoaderData, useRouteError } from "@remix-run/react";
import polarisStyles from "@shopify/polaris/build/esm/styles.css";
import { boundary } from "@shopify/shopify-app-remix/server";
import { AppProvider } from "@shopify/shopify-app-remix/react";
import { authenticate } from "../shopify.server";

import { Page, Layout,Button, Form, FormLayout, TextField, Card,RadioButton } from "@shopify/polaris";
import {useState, useCallback} from 'react';

export const links = () => [{ rel: "stylesheet", href: polarisStyles }];

export const loader = async ({ request }) => {
  await authenticate.admin(request);

  return json({ apiKey: process.env.SHOPIFY_API_KEY || "" });
};

export default function Apptopay() {
    const { apiKey } = useLoaderData();
  
    return (
      <Page
      backAction={{content: 'Settings', url: '#'}}
      title="Apptopay Configuration Settings"
      primaryAction={<Button variant="primary">Save</Button>}
    >
      <Card>
      <Form >
        <TextField label="Authentication Key" type="text" 
        align="right" />
        <TextField label="Retailer ID" type="text" />
        <TextField label="Retailer GUID" type="text" />
        <TextField label="Product ID" type="text" />
        <TextField label="Product GUID" type="text" />
 
      </Form>
     </Card>
     </Page>
    );
}

// Shopify needs Remix to catch some thrown responses, so that their headers are included in the response.
export function ErrorBoundary() {
    return boundary.error(useRouteError());
  }
  
  export const headers = (headersArgs) => {
    return boundary.headers(headersArgs);
  };

Finally I fixed it, To my knowledge I don’t know exactly what went wrong. I have already changed my entry.server.tsx file name to entry.server.ts for some other bug , and edited the code inside it.

I removed that, and changed the filename to entry.server.tsx

Here is the code for entry.server.tsx

Can someone explain the what went wrong and what is happening in entry.server.tsx file?

import { PassThrough } from "stream";
import { renderToPipeableStream } from "react-dom/server";
import { RemixServer } from "@remix-run/react";
import {
  createReadableStreamFromReadable,
  type EntryContext,
} from "@remix-run/node";
import { isbot } from "isbot";
import { addDocumentResponseHeaders } from "./shopify.server";

const ABORT_DELAY = 5000;

export default async function handleRequest(
  request: Request,
  responseStatusCode: number,
  responseHeaders: Headers,
  remixContext: EntryContext
) {
  addDocumentResponseHeaders(request, responseHeaders);
  const callbackName = isbot(request.headers.get("user-agent") || "")
    ? "onAllReady"
    : "onShellReady";

  return new Promise((resolve, reject) => {
    const { pipe, abort } = renderToPipeableStream(