MEXEM's FX liquidity providers quote currency pairs in accordance with standard industry convention which, in the case of the EUR and USD, requires entry of the pair as EUR.USD. As the industry does not support inverted quotes (e.g., USD.EUR) and the first currency listed is the one being bought or sold, converting EUR into USD requires that you sell the EUR.USD pair.
If you wish to specify your order in terms of USD to buy rather than EUR to sell, left click the Quantity field (in the Order Entry panel for Mosaic or on the order line in Classic). The quantity ladder will display. Toggle the quantity from the default currency to the alternate currency as required.
For example, if the forex pair you're trading is EUR.USD, the default currency is EUR and the quantity shown is in euros. When you toggle to the alternate currency (in this case USD) the value will default to the equivalent USD value based on the current exchange rate. Modify the USD quantity as needed and submit the order.

Additional information on cash quantity for Forex orders can be found in our Users' Guide.

For instructions on how to convert currencies in all our trading platforms, see: How can I convert currency at MEXEM?