This usually means there's a typo in the code, the code has expired, or it's already been used.
Here's how to fix it:
Double-check for typos. If you're typing the code manually, it's easy to mix up similar characters (like 0 and O, or 1 and l). Copy and paste it instead if you can.
Check the code's age. Activation codes expire after 7 days. If yours is older, you'll need a new one.
Check if you've used it before. Codes only work once. If you've already installed this code - even on another device - it's been used up.
Get a new code. Contact support via zable-SIMcard-support@zable.co.uk and we'll send you a new one at no cost.