Hmmmm... I forgot to mention I had already tried this... didn't work. I've also tried with USD/CAD and others. Can't seem to get any data on forex from TWS. Very frustrating. But like I said, I can get equities, and I can see the forex data right there in TWS.
I always get the following error: Code 200, No Security definition has been found for the request.
Right now you would need to use GBP as the symbol name, and set the asset currency to CHF in the symbol information. We have changed this so you can enter it as GBP/CHF, and we hope to release a version which includes this update soon. One thing to note is that to trade the GBP/CHF pair, your account currency would need to be either GBP or CHF. Otherwise we don't have a way to convert your profit from CHF to USD, for example. Eventually we may support using the current GBP/USD or USD/CHF rate to calculate the correct profit.