I also got 'server error' on first try. 2nd try worked and I sent a significant amount of BTG to exchange for BTC.
According to the status page the exchange went through successfully. And it states "Your money has been exchanged. Blockchain is confirming your transaction." - However when checking any block explorer it is clear they did not make any transaction (it is not in the mempool). This has been the case for hours, even though the page stated the process would complete in 30-50m.
I really hope they are not running away with my coins. I was hesitant to use them but could not find any other exchange that would take my BTG (Bitfinex, Bittrex nor Binance are accepting new users currently... so that left Changely for me)