[Urgent] Checkout Extensibility not working on production

[MiguelCirculy]

I will try to be as clear and structured as possible. 

## Context

Our team is developing a custom App to handle SubscriptionContracts. The chosen approach has been using Checkout Extensibility by creating a full page view (`customer-account.page.render`) linked from `customer-account.order`. 

The selected store to test this functionality has Checkout and Customer Accounts Extensibility preview enabled

On development

On production

.env

NODE_ENV=production
SHOPIFY_API_KEY=[HIDDEN]
SHOPIFY_API_SECRET=[HIDDEN]
ACCESS_TOKEN_SCHEMA_FETCH=[HIDDEN]
SCOPES=[SAMES SCOPES AS IN PARTNERS]
PROXY_API_URL=[NGROK PROXY]
SHOPIFY_API_VERSION=2023-07
SHOPIFY_APP_URL=[HIDDEN]
WEBHOOK_URL=[HIDDEN]

 
shopify.app.toml

client_id = [HIDDEN]
name = [NOT RELEVANT]
handle = [NOT RELEVANT]
application_url = [OUR INSTANCE]
embedded = true

[build]
automatically_update_urls_on_dev = false
dev_store_url = "circuly-app-dev-checkout-ui.myshopify.com"
include_config_on_deploy = true

[access_scopes]
# Learn more at https://shopify.dev/docs/apps/tools/cli/configuration#access_scopes
scopes = "read_fulfillments,write_fulfillments,read_customers,write_customers,read_shipping,write_shipping,read_orders,write_orders,read_products,write_products,read_customer_payment_methods,write_own_subscription_contracts,read_own_subscription_contracts,write_orders,read_orders,write_purchase_options"

[auth]
redirect_urls = [
  "[OUR INSTANCE]/api/auth/callback",
  "[OUR INSTANCE]/api/auth/shopify/callback",
  "[OUR INSTANCE]/api/auth/callback"
]

[webhooks]
api_version = "2023-07"

  [webhooks.privacy_compliance]
  customer_deletion_url = [NOT RELEVANT]
  customer_data_request_url = [NOT RELEVANT]
  shop_deletion_url = [NOT RELEVANT]

[app_proxy]
url = [OUR INSTANCE]
subpath = "css"
prefix = "apps"

[pos]
embedded = false

## The issue 

Everything is working fine on development, after running `pnpm run dev`, making sure that we are adding our app to the correct store (which has the Checkout Extensibility enabled). 

When we deploy our app and we install it in the same store, extensions are just not shown. 
We kindly ask for help since this issue has got us stuck for a while. Our guesses are: 

- Shopify Plus plan does not allow you to see the Checkout Extensibility. We are aware of this as specified in the docs, but we are deploying our app to a development store. Does this even matter? 

- We are missing something else.

Again, we kindly ask for help from the Shopify staff. What should we check on here?

Kind regards,
The Circuly team