Referral
After you buy, the vault shows a code. Someone who checks out with it gets 10% off the electrician kit. You get a note on the order in admin — not cash, and not a second free kit.
Buy first, then share the code from the vault. A link looks like /checkout/?ref=RXXXX.
Example shape: your-code. Codes that do not match a real order do not discount the price.