Using a 16-digit online calculator is relatively straightforward:
(This would be followed by an input box and a "Generate" button on your actual page.) Zte Modem Dongle Unlock Code Calculator -16 Digit- Online
input, select width: 100%; padding: 14px 18px; font-size: 1rem; border: 2px solid #cbdbe0; border-radius: 36px; background: white; transition: 0.2s; outline: none; font-family: 'SF Mono', 'Fira Code', monospace; font-weight: 500; select width: 100%