ERR_NGROK_SHIP_POOL_NODE_POOL_OS_ID_ILLEGAL_CHARACTER: The 'node_pools[INDEX].os_id' value VALUE must be a whole number - ngrok documentation

What does ERR_NGROK_SHIP_POOL_NODE_POOL_OS_ID_ILLEGAL_CHARACTER mean?

ngrok returns ERR_NGROK_SHIP_POOL_NODE_POOL_OS_ID_ILLEGAL_CHARACTER with this message:

The 'node_pools[<INDEX>].os_id' value <VALUE> must be a whole number.

Where can I get more help with ERR_NGROK_SHIP_POOL_NODE_POOL_OS_ID_ILLEGAL_CHARACTER?

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