Your order filled at a slightly different price than the quote you saw — that's slippage, and it's normal. Three things cause it: the bid-ask spread, fast-moving prices, and your order type. None of them means anything broke.

The bid-ask spread

The “quote” you glanced at might have been the mid or the last trade — but you buy at the ask and sell at the bid. So a market buy fills at the ask, which is above the mid, and it looks like you “paid more.” You didn't get a bad deal; you just paid the spread, which is always the cost of immediacy. On a wide-spread strike, that gap is bigger.

Fast prices and order type

Fast markets: in the milliseconds your order travels, the price can move — so a market order fills at whatever's available now, which may differ from the quote a moment ago. Order type matters: a market order prioritizes speed (accepting price uncertainty); a limit order guarantees your price or better (but may not fill). The tradeoff between the two is the tradeoff between certainty of fill and certainty of price.

The quote is a snapshot; the fill is reality a heartbeat later. The difference is the spread and the market moving — normal, not a glitch.

The quick takeaway

Fills differ from quotes because of the spread (you cross it), speed (prices move), and order type. It's slippage, and it's why you factor it into your risk math and trade liquid strikes. NoVo's adaptive routing works to minimize slippage — but no tool can promise the quote, because the market has the final say on the fill.