For next time, after redeeming the voucher, you will immediately get a queue number. My experience is that I bought a voucher, redeemed it, then went to the Lab. Damn the queue is long. You know that, I didn't redeem first. In the end, I didn't use it, I moved to the Lab near the Direct Lab, and paid again.
Kapok buying Antigen vouchers through apps. Better go show