Question: Why can I not trade micro lots (volume under 0.1 lots) on MT4?
Please note that for premium accounts, the minimum trading volume is 0.1 lots.
If you wish to trade micros, then you need to transfer funds to another account that will have a balance of under 2500 USD.
If the reason of not being able to trade micro lots are the above, the symbol you like to trade might have restrictions of trading volume.
You may check the contract specifications from the official website to find out more.