Almost every “invalid code” message has a reason behind it, and in most cases the reason was written down somewhere before you clicked. Having read the terms behind thousands of offers, the same handful of causes come up again and again. Here is what actually goes wrong, and what to look for before you spend time filling a basket.

1. The code was never open to everyone

This is the most common one by a distance. A great many discounts are conditional, and the condition is often dropped when the offer gets passed around:

  • Student discounts normally need your student status verified through a third party before the code will work at all.
  • Newsletter codes are sent to your inbox after you subscribe. The code circulating publicly is often somebody else’s single-use version.
  • New customer offers check whether your email or address has ordered before. If you have an account, the code will not apply.
  • Referral codes usually reward your next order rather than the one you are placing now.

If a listing anywhere says simply “15% off” and the retailer’s own site says “15% off for students”, the listing has dropped the part that matters.

2. It excludes the thing you are buying

“Full price only” is the exclusion that catches most people out, because it fails at exactly the moment you think you are being clever — stacking a code on top of sale items. Charles & Keith’s student discount, for example, applies to full-priced items only, so it will not reduce anything already in the sale. Plenty of codes also exclude specific brands, gift cards, or anything already discounted.

3. You have not reached the minimum spend

Spend-and-save offers are conditional by definition: “£10 off when you spend £100” does nothing to a £90 basket. Free delivery works the same way and the thresholds vary widely — Evolution Slimming set theirs at £25, Sweatband.com at £50, Charles & Keith at £75. A “free delivery” claim with no figure attached is worth checking before you rely on it.

Watch for geography too. Sweatband.com’s free delivery covers most mainland UK postcodes — England, Scotland and Wales — which means the Highlands, islands and Northern Ireland may not qualify.

4. It has simply expired

Retailers withdraw codes without announcing it, and seasonal codes linger online long after the season. If you find a code named after a holiday that has been and gone, treat it as dead until proven otherwise.

5. The “code” was never a code

Some listings are not discounts at all. A price — “from £12”, “just £5” — is a shelf price, not a saving, and no code exists to enter. Neither is “pay in 3 interest-free instalments”: spreading the cost of an order does not change what the order costs.

A quick checklist

  1. Does the offer name a condition — student, new customer, newsletter, referral? If so, does it apply to you?
  2. Is there a minimum spend, and does your basket clear it?
  3. Are your items full price, or already reduced?
  4. Does “free delivery” state a threshold and a region?
  5. Does the discount actually appear in the order total before you pay?

That last point is the one that matters most. Enter the code, then check the total changed. A code that silently does nothing is far more common than an error message, and it is the reason to look at the figure rather than the confirmation.

Terms change without notice, and the retailer’s own wording is always the final word. If you find an offer on this site that does not match what the shop says, tell us on the contact page and we will check it.