I make request to https://api.sandbox.ebay.com/buy/browse/v1/item_summary/search?q=beatles and get Error 500. I make the same request to non-sandbox (aka production) and behold! Results!
So the sandbox api is broken atm...? I cannot find any status page, there is only premium support available for $75 per hour... Are you guys being serious here? The error message even says I should contact ebay developer support. Maybe add an email in the message next time?