The error 'Coin temporarily unavailable at exchange' means that the crypto exchange you are connected to is temporarily unable to process requests for that coin. This is caused by the exchange, not by Cryptohopper.
Cause
This error typically occurs when your exchange is experiencing high traffic or performing scheduled maintenance. During those moments, certain coins become temporarily unavailable for trading.
What to do
You don't need to do anything. Cryptohopper has no control over this — the exchange will resolve it on its own. Check your exchange's official announcements or status page for updates on when trading will resume.