#SPX1 DTE I sold this morning the 5/23 4025/4045 put at 1.35. Looked fine and I had an order to close at .10 since I had to be away from screen mid afternoon. Near the end of day I checked prices and S&P sinking. Put a market order to close at 3:52. NEVER got filled. Luckily S&P closed at 4145.67. Market order does not guarantee execution!!! Who knew, not me.