You need to specify the user :
// Revoke a specific user token
Auth::user()->tokens()->where('id', $id)->delete();
// Get user who requested the logout
$user = request()->user(); //or Auth::user()
// Revoke current user token
$user->tokens()->where('id', $user->currentAccessToken()->id)->delete();
Update of Laravel 7, 8, 9, 10 :
// Revoke the token that was used to authenticate the current request...
$request->user()->currentAccessToken()->delete();
// Revoke a specific token...
$user->tokens()->where('id', $tokenId)->delete();