PAPI-3173 - Update customers.mdx to correct code block syntax and improve clarity in JWT payload examples

Author: krzysztof-maziarka-bc

docs/storefront/headless/customers.mdx

@@ -27,7 +27,7 @@ We recommend using the login mutation and customer access token because this com
 
 If using the customer access token, then you just need to use the `createCartRedirectUrls` mutation and use the redirectUrl provided there. It will be a session sync link that will copy data from the headless storefront to the BigCommerce-hosted page. This approach simplifies session synchronization and offers consistent login states.
 
-```js "Generate redirectUrl example" showLineNumbers copy
+```graphql "Generate redirectUrl example" showLineNumbers copy
 mutation createRedirectUrl($input: CreateCartRedirectUrlsInput!) {
   cart {
     createCartRedirectUrls(input: $input) {
@@ -43,15 +43,15 @@ The other option is when a customer signs in to your headless storefront and you
 
 You can sign a customer in to an embedded checkout by using the session-sync URL from the [createCartRedirectUrls mutation](https://developer.bigcommerce.com/graphql-storefront/reference#definition-CartMutations).
 
-```js filename="Example JWT payload" showLineNumbers copy
+```json filename="Example JWT payload" showLineNumbers copy
 {
-  "iss": {{CLIENT_ID}},
+  "iss": "{{CLIENT_ID}}",
   "iat": 1535393113,
-  "jti": {{UUID}},
+  "jti": "{{UUID}}",
   "operation": "customer_login",
-  "store_hash": {{STORE_HASH}},
-  "customer_id": {{CUSTOMER_ID}},
-  "channel_id": {{CHANNEL_ID}},
+  "store_hash": "{{STORE_HASH}}",
+  "customer_id": "{{CUSTOMER_ID}}",
+  "channel_id": "{{CHANNEL_ID}}",
   "redirect_to": "/cart.php?embedded=1&action=loadInCheckout&id=bc218c65-7a32-4ab7-8082-68730c074d02&token=aa958e2b7922035bf3339215d95d145ebd9193deb36ae847caa780aa2e003e4b",
   "request_ip": "111.222.333.444"
 }