Adding Automation to an Online store

Current situation : 1- our online store is up and running. we are using WordPress along with woo-commerce. and couple of other plugins. 2- we are selling digital gift card with email delivery. ( the product sold is 10 digits send by email ) 3- the process of sending the gift card code ( 10 digits ) is manual. whenever the invoice is paid by the customer, we are manually sending the code to the customer's email. 4- we have only 10 products. with future plan to add more to reach 25 products all digital. 5- each gift code can be used once, so for each new order we will be sending new code. The Goal : 1- we want to make the process automatic. whenever an invoice is settled the code should be automatically sent to customer along with the invoice or in separate email. Scope of work: 1- the bid winner should be able to perform the job in a professional way that doesn't affect the Store, so all the testing should be in an offline mode and after approval from our side the bidder can implement on the live server. 2- the bidder is free to create a plugin, code.... the most important this is the simplicity and the ease of development in the future. 3- there should be a very secure place where we can store the gift code list for each product. 4- the code should be deleted from our list. since it cant be used twice. ------------- if anyone has a better idea bout how to move the processed from manual to automatic is free to discuss it with me. hope that i can get your good offers with the scope of work. regards