The minimum withdrawal amount for Tron Network (USDT TRC-20) is 11 USDT. When you make a withdrawal, your Gross Withdrawal Amount (before fees) needs to be at least this amount. 

Why am I seeing "Invalid withdrawal amount: Min amount 11000000"? 

The error message returns the amount in its lowest denomination rather than in the display number. The scale between the two is 6 so 11000000 is the same as 11 USDT.