After you have beat wake in pastoria city you have to fly to hearthome city and you can battle the 5th gym leader and get your 5th badge.
In Pokemon Red, the fifth badge is possessed by the Poison-Type Koga. The badge is named Soul Badge. It lets you use Surf outside of Battle.
Petalburg City.
Hearthome
Fuschia city.
hearthome city
Hearthome City.
Beat the gym leader
The fifth gym leader in Pokemon platinum is crasher wake but you get the fourth badge.
You need to defeat Koga in Fuchsia City to get the 5th badge, the Soul Badge.
The fifth badge is in Sootopolis City, you need Surf, Dive, and Whirlpool to get it
Trade a Pokemon from an old version and make sure you have the fifth badge.
you should use either ground or psychic Pokemon