Check that GMVify Post Purchase is chosen under Post-purchase page in your checkout settings, that the offer is turned on and scheduled for now, and that its rules (products, collections, tags, order total, item count or country) match the order.
Shopify doesn’t show a post-purchase page for every payment method or order; those orders go straight to the thank-you page.
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.