This problem can have multiple causes. Please first check the following steps before sending in a support ticket.
Please verify your base currency
Please check in your assets if you have enough of your base currency (Please check your exchange for the most up-to-date minimum required amount per order)
"Total base currency (BTC, ETH, USDT) in assets on exchange", which you can see on the dashboard, reflects the total worth of your assets, not the amount of base currency.
If you exchange's minimum is 0.01 BTC, and you fill in 0.01 BTC as the minimum, this could result in errors. Fees are subtracted when making an order. If the total is below 0.01 with fees subtracted your order cannot be made. Please set your minimum to a value slightly higher than the minimum of your exchange.
Exchanges could have changed the minimum order requirement. Please verify if your minimum order requirement is still correct.