Sorry to hear you are having trouble with your order button. First, I would double check that you have the Oberlo Google Chrome extension as this is required to see it.
If you still can't, I would double check that your orders in Shopify are not fulfilled. If they are fulfilled, you will need to go to the order in Shopify and under Fulfillment press More > Cancel Fulfilment. Then, when you go back to your Oberlo orders page you'll be able to see it.
If you'd like an extra set of eyes to double check it, please feel free to reach out to our support team at firstname.lastname@example.org. They can log in and have a look for you too. Let us know how it goes!