Order IDs are unique to each store or even order. You will usually receive either a email or SMS confirmation when you've successfully made an order on the partner store's website or app. The Order ID should be available in the email or SMS. Alternatively, it may appear in your account (in purchase history) on the merchant's website or app.
If you have lost or are unable to find the order ID, you can email the store to retrieve it.
You can view the samples for Order IDs by clicking here.