Discount codes are created when a customer opens an email for the first time.
It is possible that customers are opening emails that were previously sent before the discounts were removed from your email templates.
For example, if an email with discount code was sent out on March 1st, but the customer did not open the email until March 13th, then the discount code will be generated on the 13th. This code will run for the allocated time of your discount codes that was configured in the UpOrder App. If this was for 7 days, the customer will be able to use this code until the 20th.
Kindly note that Shopify limits to one discount code being used per transaction (unless otherwise configured through other apps), so your customers cannot stack discount codes when making purchases from your store. You also have the option to manually disable these codes in the Shopify backend as well!
Please reach out to [email protected] or through the in-app chat if you have any questions!