In case you enter a discount code during checkout that doesn't exist or isn't currently active, then you can see the message: “Unable to find a valid discount matching the code entered”.

To use the elegoo coupons on their website, you need to meet the conditions:

•  The items you choose must meet all coupon requirements as explained in the Terms and Conditions.

• The coupon has not expired. 

• The seller uses the elegoo checkout system or a customized checkout system that accepts the coupon.

To avoid this problem, you should check out carefully elegoo promo code before that promo code could be expired, some promo codes are tied to a minimum purchase, a first-time purchase, or tied to geography, and other reasons.

Usually, Coupon Stacking is not allowed at elegoo. However, the store will surely give out notice if available.

Yes. Coupons for each Discount Event of elegoo will be collected here while being updated day by day. Sometimes, there will be deals not updated promptly but it's rare, we expect sympathy from you. 

Yes, it has ever. It may not be available now, but it is completely possible for loyal customers of elegoo to get it by tracking all of its promotion programs.