Check that the order is still open for editing: it hasn’t shipped, fulfillment or production hasn’t started, it doesn’t have your lock tag, nobody locked it, and it’s within the time you allowed.
Then check that the setup guide shows the customer account and thank-you page steps as done.
Still stuck?
Open the app in your Shopify admin, go to Help and click Chat with us, or email [email protected] with your store’s myshopify.com address.