ERR_NGROK_SHIP_POOL_NODE_POOL_ZONE_CONFLICT: The 'node_pools[INDEX].zone' value ZONE is not in region REGION - ngrok documentation

What does ERR_NGROK_SHIP_POOL_NODE_POOL_ZONE_CONFLICT mean?

ngrok returns ERR_NGROK_SHIP_POOL_NODE_POOL_ZONE_CONFLICT with this message:

The 'node_pools[<INDEX>].zone' value <ZONE> is not in region <REGION>.

Where can I get more help with ERR_NGROK_SHIP_POOL_NODE_POOL_ZONE_CONFLICT?

Email support@ngrok.com and include the error code.