'Method not allowed' when attempting to follow the documentation

[asandler]

Hey guys,

I'm trying to follow this documentation: https://shopify.dev/api/examples/order-editing#how-it-works 

But with every one of the queries on the doc I get a 'Method not allowed' response, though it's being done through a POST request. I've already queried other GraphQl endpoints so I know I'm requesting correctly. Maybe my query body is wrongly structured?

For example the 'Begin Order Edit' request:

import { postGraphQl } from "../graphQl/postGraphQl";

export const postOrderBeginEdit = async (shop, accessToken, orderId) => {
  const body = `
  mutation {
    orderEditBegin(
      id: "gid://shopify/Order/${orderId}"
    ) {
      userErrors {
        field
        message
      }
      calculatedOrder{
        id
      }
    }
   }`;

  return postGraphQl(shop, accessToken, body);
};

I have also tried adding the 'write_order_edits' permission as mentioned in the docs but still no changes.