You need to activate the app embed block for the Subify widget to be displayed on your product page.
Please go to Shopify Admin > Online Store> Theme> Customize> Theme Settings make sure that the Subify app embed is on, then click on the “Save” button as well.
The subscription widget should now appear on your product page, you've created a subscription rule for it.
Now that the widget is available, you can have a “test payment” which Shopify itself has a guideline on.
You can use “Test Payment” to test how your customers pay for their orders and to test how the app processes those orders.
You better know that some themes require a little extra attention to get Subscription Widget Setup. In that case, please contact our support. We’ll be so happy to assist.