I have a real and a paper IB account. The real account has market data subscription, just subscribed today, which I shared with the paper account. I confirmed that data subscription was working by logging into TWS and seeing the price and options chain data.
I logged into the IB Gateway desktop app, see that API Server status is "connected".
I open up TradeTest on Zorro, click Test, then Trade and it says SPY unavailable, and logs out. Clicking Trade a few more times generates the same message and sometime a message about no market data, but not all the time.