Your training with weapons allows you to use the mastery property of Greataxes:
Cleave. If you hit a creature with a melee attack roll using a Greataxe, you can make a melee attack roll with the Greataxe against a second creature within 5 feet of the first that is also within your reach. On a hit, the second creature takes the Greataxe’s damage, but don’t add your ability modifier to that damage unless that modifier is negative. You can make this extra attack only once per turn.
Cleave (Halberd)
Action Type:
1 Action
Range/Area:
--ft. Reach
Your training with weapons allows you to use the mastery property of Greataxes:
Cleave. If you hit a creature with a melee attack roll using a Greataxe, you can make a melee attack roll with the Greataxe against a second creature within 5 feet of the first that is also within your reach. On a hit, the second creature takes the Greataxe’s damage, but don’t add your ability modifier to that damage unless that modifier is negative. You can make this extra attack only once per turn.
That's a known issue, but I've let the devs know it came up again.
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