You can't enter them manually. But, check out 39clues.wikia.com/wiki/Card_combos
~James the Janus
Check out this reusable card code! P3GJW7JEXP
Yes
P23hrfxfxp
madrigals
LUCIANCLUE
P23hrfxfxp
P3NCKRWNXP unused
Tomas
CROATIA
The hidden code on card 28 in the 39 Clues collection from the first book is "Salamander."
William McIntyre's dog in the 39 Clues book series is named Saladin. Saladin plays a significant role as a companion to William and the Cahill siblings throughout their adventures.
Here it is:p24nxknmxp
universe.skylanders.com/play