Observe: That is an add-on. You will need to have no less than WooComerce PDF Vouchers v3.9.1 to make use of it.
WooCommerce PDF vouchers: OTP Verification addon lets you ship OTP (As soon as Time Passcode) both on electronic mail or cell on voucher code redemption.
= model 1.0 (2019-08-05) =
* [+] Preliminary Launch