You sent a market order while the market was actually closed, so it could not be executed at the time. RH was protecting you from getting a fill far away from t

You sent a market order while the market was actually closed, so it could not be executed at the time. RH was protecting you from getting a fill far away from the last price, because the stock gapped up massively that Monday. 264.77 was the close on Friday, and 305.77 was the open on Monday. You should be thanking them, because otherwise your position would be around $45 under water by now. Never use market orders outside of regular trading hours; you have no idea where you are going to get filled.