cannot enter four-digit passcode on keypad

on my keypad, I have the green light illuminated, which I understand means I have a charged battery. And I have the blue light illunminated which means that I am in the disarmed mode. When i press in my four-digit pass code, nothing happens. I am able to change the status from "disarmed" to "away" using my iPhone, but I cannot do so on the key pad. Am I supposed to press come other key first? I am sure that there is an easy explanation, but for all of the FAQs and videos, I cannot find one.