Ensure your Pokémon Brilliant Diamond software is updated to version 1.3.0 or higher.
: Following the weaponized duplication glitches that impacted early builds of the game, ILCA integrated passive checks. Cloned or heavily modified Pokémon are blocked from being traded through the GWS network. 3. General Gameplay Fixes and Stability pokemon brilliant diamond 1.3.0 update
For competitive players, 1.3.0 was a pivotal moment. It marked the end of the "Series 1" rules and the beginning of "Series 2." Ensure your Pokémon Brilliant Diamond software is updated