25% off Promo code gave 100% off to the customer. Where's the error

Shopify Discussion
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Topic summary

  • Issue: A 25% off promo code applied as 100% off for one customer at checkout, and the customer was charged only for shipping. The discount was intended to apply 25% off the entire order.
  • Checks: The merchant reviewed the discount settings and the specific promo code in detail and found no errors. Nothing in the configuration appears to explain a full discount.
  • Reproduction: Multiple other people tested the same code on different devices, and it correctly applied 25% off for them. The problem appears isolated to a single customer and session.
  • Concern: The merchant asks whether the system could be hacked or otherwise manipulated. Guidance is requested on how this could happen and how to resolve it.
  • Status: No confirmed cause or fix yet, and the discussion remains open with unanswered questions.
Summarized with AI on January 5. AI used: gpt-5.
1

I gave a promo code to the customer (25% off entire order), and at the checkout when he applied this promo code it gave him 100% off and he was only charged for a shipping.

I checked the discount settings, I checked this particular promo code thoroughly - there’s no any mistakes, everything is correct. Moreover, I asked different people from different devices to apply the same promo code - it worked normally for all of them, giving them 25% off as it supposed to be.

I really don’t know how’s this possible and how can this be solved? Is it possible to hack the system like this?

Regards,

Aleks