You're attempting to render a <Reorder.Item> component.

<Reorder.Item />

You're receiving a message that Reorder.Item must be a child of Reorder.Group. This means you either haven't rendered a Reorder.Group, or you've rendered Reorder.Item outside of your Reorder.Group.

Solution

Ensure any Reorder.Item component is rendered somewhere within a Reorder.Group component:

<Reorder.Group>
  <Reorder.Item />
</Reorder.Group>

It doesn't need to be a direct child. This is also okay:

<Reorder.Group>
  <div>
    <Reorder.Item />
    <Reorder.Item />
    <Reorder.Item />
  </div>
</Reorder.Group>