Limit orders


I noticed when I wanted to create a limit order, the app give notice I place an order for “0” shares. In this particular case the limit price was $340 or €290 while the cash available was slightly above €300. After checking with the helpdesk, it turns out for US stocks you need to have a 5% buffer above the current ask-price “in order to ensure the order can be fulfilled”. However, this logic doesn’t make a lot of sense as the entire purpose of a limit order is to know exactly what you’ll pay. Ofcourse, there has to be some kind of metric to account for FX-rate changes but 5% seems a little bit excessive. Anything what can be done about this?