Pokemon diamond why the Karate Kid did not give me the odd keystone?

In Pokémon Diamond, The Karate Kid, also known as the NPC in the Fighting Dojo, will only give you the Odd Keystone if you have completed certain conditions. Specifically, you need to have the right requirements, such as having a Pokémon with you that can use the move "Surf" or having the Odd Keystone itself in your inventory. Make sure to revisit him after fulfilling any necessary criteria or check if you have already obtained the Odd Keystone from another source.