Sometimes US companies get delisted from the exchange and begin to be traded on the 'OTC' market (Over The Counter). This can happen if the company is not compliant with the exchange for example. 

Unfortunately BUX does not have direct access to OTC market data and therefore can not offer trading in such circumstances. In such situations we will aim to inform impacted clients via email as soon as we become aware of the situation, clearly mentioning the date on which it is set to happen. We will inform you that we will be forced to sell your remaining shares before they delist from the exchange, unless you update us and specifically request that we do not take action. By holding on to shares in such situations can mean you will not have any future opportunities to sell your shares.