## Is your feature request related to a problem?

Right now, if you try to invite someone who's already invited (or a user) you get the following error message:
![image](https://user-images.githubusercontent.com/1727427/98357556-adff4a80-2025-11eb-9f4d-ba748155d036.png)

## Describe the solution you'd like

The server itself does return a useful error message, so we could just display that

## Describe alternatives you've considered



## Additional context



#### *Thank you* for your feature request – we love each and every one!

posthog/api/test/test_organization_invites.py
self.organization_membership.level = OrganizationMembership.Level.MEMBER
        self.organization_membership.save()
        invite = OrganizationInvite.objects.create(organization=self.organization)
        response = self.client.delete(f"/api/organizations/@current/invites/{invite.id}")
        self.assertEqual(
            response.data,
            {
                "type": "authentication_error",
                "code": "permission_denied",
                "detail": "Your organization access level is insufficient.",
                "attr": None,
            },
        )
        self.assertEqual(response.status_code, 403)
        self.organization_membership.level = OrganizationMembership.Level.ADMIN
        self.organization_membership.save()
        response = self.client.delete(f"/api/organizations/@current/invites/{invite.id}")
        self.assertIsNone(response.data)
        self.assertEqual(response.status_code, 204)
        self.assertFalse(OrganizationInvite.objects.exists())