Cannot open Apollo Server (`/graphql`) on a Deployed Strapi CMS

I am building a Strapi CMS with the GraphQL plugins. On my local development environment, I can access the GraphQL frontend using localhost:1337/graphql. However, when I deploy it on render.com, the /graphql route always return the following.

Welcome to Apollo Server 
The full landing page cannot be loaded; it appears that you might be offline.

However, I can still access the GraphQL API by a POST request to /graphql (on Postman and on my own Frontend App). In other word, the GraphQL API is accessible, but I cannot enter the GraphQL Playground (the frontend part).

I am not sure why this is happening.
I expected to be able to access the /graphql route on my render deployment.

My deployed app is here peak-post-strapi.onrender.com/graphql.

How to Recreate The Error

– Just build a new strapi app with default contents
– Install the strapi GraphQL plugins
– Deploy it on [render.com](https://stackoverflow.com)
– You should find that the `/graphql` part on render deployment is not accessible, while on it is accessible on local development environment.