Planet Code is an older USPS barcode for tracking mail - the opposite of PostNet, with mostly tall bars where PostNet has short ones. Since 2013 the USPS has asked for the Intelligent Mail barcode instead.

What it holds
Characters	Digits only.
Length	11 or 13 digits.
Check digit	Always there, worked out by Labeljoy. It's in the bars, not in the readable text.
Readable text	The digits, under or over the bars.

The rest of the settings - text position, quiet zone, color - are in the Barcode section.

What goes wrong
Invalid input data length.	The value isn't 11 or 13 digits long.
Numeric only data expected.	The value has something other than digits.