kraken unknown asset pair

I am trying to do a market sell order on the Kraken marketplace via the unified api method: 
`
createMarketSellOrder()`

I've tried the pairs:
```
BTC/BCH
XBT/BCH
ETH/BCH
```

And none have worked. Each time the `createMarketSellOrder()` method returns an error like: 
`{ error: [ 'Equery:Unkown asset pair' ] }`

Any way around this?
