D-Link AC750 User Manual page 44

Section 3 - Configuration
If you selected Automatically, the summary window will display
your settings. Write down the security key and enter this on your
wireless clients. Click Save to save your settings.
If you selected Manually, the following screen will appear. Create
a passphrase for your security password. Click Next to continue.
You will see the Setup Complete screen like the one above.
Note: The security password/passphrase must be between 8 and 63
characters and is case-sensitive. You will need to enter this passphrase
on your wireless clients exactly or it will not connect.
D-Link DIR-818LW User Manual 39