Discount codes are mainly used for one-time purchases. If you have items in your cart that are set for subscription, ie: every 1 week, every 1 month etc.the likelihood is that your discount code will show you an invalid code message when you enter it.
If you have been given a discount code that is specific for subscription orders then it will work for you at the checkout stage of a subscription order.
How to fix this
Remove any items from your cart that are set for a subscription.
Add the items back to your cart as one-time purchases.
Complete the checkout process.
Enter your discount code on the payment page.
Enjoy your discount you lucky customer for life!
If you would like to subscribe and use your code at the same time, contact us and we may be able to authorise your code for a subscription order.