These are the type of vouchers:
Sign up vouchers
All vouchers have an expiry date of 60 days from the date of issue. The app will remind you of the expiry date, 7 days before.
Sign up vouchers are those that you get when you sign up using a referral code or referral link. These would be 3 vouchers.
Invite vouchers are what you are given when your direct invite makes their first purchase. When you invite someone and they download the app through your link, they will automatically get 3 sign up vouchers and you will get 1 pending invite voucher. Once your invite makes their first purchase, this pending voucher will become an active one.
If your direct invite does not make their first purchase within 60 days, your pending voucher expires.