Since bookings are for services and not products, there really isn't a need to "fulfill" an order (which is mainly used for products and getting that product to a warehouse and shipped).
You could just leave those orders as unfulfilled in Shopify. You can also fulfill them on Shopify if you want, of course. From the order status and bookings perspective, fulfillment it doesn't change anything.
Or, you could use another app to Automatically Fulfil Digital Products in Shopify Orders.
Please have a look at these docs; we found: