This error will be displayed to your customer at the BATM when a transaction fails for any reason. There are many possible reasons behind it, but the generic message displayed is for the Operator’s (your) protection. This is to prevent giving away any information that might be used against you during an attack on your BATM network.
You are out of coin: check your wallet & Exchange balances.
Your wallet or Exchange is down: check with your provider for their API status.
The transaction amount is insufficient: make sure you set a high enough minimum.
If your settings stopped working suddenly, please contact your provider first.
SELL: When using "Strategy 2: sell coin on the Exchange", always bear in mind that the Exchanges will require a minimum of X confirmations before it will permit you to sell the customer's coin. Thus, you should keep enough BTC in your Exchange wallet to satisfy the immediate SELL amount a customer may submit. This will help prevent "NOT ENOUGH COINS ON EXCHANGE" transaction errors.