Hi, @Robert_Smith_UK
Thanks for posting. I hope your day is going well!
What a great idea using your eBay sales as a way to promote your Shopify business!
There are a few ways to achieve what you’re looking for but are ultimately personal preference. The first option is to create these codes manually when you receive an order. This will allow you to create new codes that are limited use. You can then add the codes to your flyer as needed. The issue with this is if you do a high volume of sales on eBay this could become tedious.
If you’re looking to generate single use codes in bulk as you have a high volume of orders, you can use an app such as VP: Discount Code Generator which is completely free.
The only issue with the above options is there is no easy way to input the codes into your flyer. My guess would it would need to be done manually.
I hope that helps! In the meantime, I’d love to take a look at your store. If you have a moment please provide your domain address.