---
title: "CORS: Cross-Origin Request Blocked"
canonical: "https://support.apollographql.com/space/ETKB/625508386/CORS%3A%20Cross-Origin%20Request%20Blocked"
format: markdown
---
When you first attempt to connect a GraphOS cloud router to your GraphQL endpoint, Studio might display an error like the following:

```
Endpoints need to be available on the public internet. Please deploy your API before continuing.

```

Additionally, messages like the following might appear in your browser's developer console:

```
⚠️ Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://localhost:9000/. (Reason: CORS header 'Access-Control-Allow-Origin' missing). Status code: 204.
⚠️ Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://localhost:9000/.
(Reason: CORS request did not succeed). Status code: (null).

```

Errors like these are usually related to Cross-Origin Resource Sharing (CORS). To resolve them, modify your GraphQL endpoint's `access-control-allow-origin` header to allow requests from `https://studio.apollographql.com`. Consult your server library's documentation to learn how to modify this header.

If you’re new to Apollo Studio, [learn how to configure CORS in this tutorial](https://www.apollographql.com/docs/apollo-server/security/cors/#configuring-cors-options-for-apollo-server).