Same here with a game I purchased yesterday. I've emailed and waiting for a response. They seem to be active on social media and the forum so hopefully they'll sort us both out soon.
Well its second day im waiting for this to get fixed if its not fixed by friday im gonna refund cause i seen this error exist everywhere i search:''Error 500'' is not making me redeem my code and no one in Indiegala cares to fix it for years...