There is no maximum amount for Market Switch orders. However, if your Switch order exceeds the balance in the Switch Pool, your order will not be processed.
The minimum amount you can order depends on the crypto pairs as follows:
BTC →
ETH : 0.00025 BTC
USDT : 0.00005 BTC
USDC : 0.00005 BTC
XRP : 0.00005 BTC