"send_paywalled_preview" value is missing

[suhan1996]

          Great!

One thing for it to work: "send_paywalled_preview" value is missing, so currently there's no emails sent out to non-paid members if the paywall is added, which is essentially the main reason for this feature (send preview version to non-paid members).

Originally posted by @suhan1996 in https://github.com/ma2za/python-substack/issues/22#issuecomment-1863221745