I believe that you have to have a phone on which you can receive the QR code, or a similar device, because you have to scan the code in order to choose and open a locker.
I don't think you can print a label and scan that.
All inpost mentions of labels state 'digital label' so I assume you don't produce or print an actual label.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)