Add an product already existing on Shopify - make sure the product contain SKU
This is important first step - associate product SKU with Activation Codes or File to download.
If customer can download file after purchased the product, then will need to upload an file for customers to download
There is option to enter it manually one by one
Or bulk upload using CSV, the content of the CSV need to be in the following format
The above will associate the activation codes with the selected product
Go to App Admin > Select Entry > Email to customer, make sure the content is correct/suitable.
Go to App Admin > Select Entry > Change status from Draft to Live
Don't forget to make sure there are activation codes associate with the selected product/entry
Do a live test order to see the whole thing in action.
Place an order with the above product, then make sure the order is paid.
Then you should receive an email with activation code for that product