IOTA, page-9

Another thing you all need to be aware of IOTA withdrawal at Coinspot is that they only allow whole numbers of MIOTA with a withdrawal fee of 0.5 MIOTA. When you place your buy order please make sure to buy IOTA as XXX.5 e.g., 125.5 etc.
In this way when you try to withdraw it to your personal IOTA Wallet (Light Node) you can withdraw the whole number e.g., 125 and they deduct 0.5 as transaction fee. This way you will not have any remainders at Coinspot.

I was able to transfer IOTA in decimals at Bitfinix but Coinspot doesn't allow. I have noticed the same whole number restriction applied to TRX withdrawals at Coinspot whereas decimal withdrawals are permitted at Binance for TRX.