D-Link AC1750 User Manual page 50

Section 4 - Security
PIN: Select this option to use PIN method. In order to use this
method you must know the wireless client's 8 digit PIN and click
Connect.
PBC: Select this option to use PBC (Push Button) method to add a
wireless client. Click Connect.
Once you click Connect, you will have a 120 second time limit to
apply the settings to your wireless client(s) and successfully establish
a connection.
Click Wireless Status to finish. This will take you to Wireless Status
screen.
D-Link DIR-868L User Manual 45