Land Sales
Only Advanced Worlds and Mega Worlds Dedicated Servers support land sales.
Therefore, if you downgrade an Advanced or Mega Dedicated-Server World to a Starter or Standard World then:
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Downgrading an Advanced or Mega Dedicated-Server World to a Stored World doesn't result in losing features immediately. If you later upgrade the Stored World back to an Advanced or Mega Dedicated-Server World then land sales will be available again, and any parcels that had been sold in the past will remain sold. However, if you upgrade the Stored World to a Starter or Standard World then you will lose the features as described above.