Why did the options order fail to execute?

Options orders may fail to execute for the following reasons:

1. Asynchronous quotes between different exchanges may cause orders to fail to execute in time;

2. Different exchanges have different minimum price movement units;

3. Due to the existence of combination orders for options, single-sided buy or sell orders may not necessarily execute. For example, for a certain TSLA option with a bid of 5.50 and an ask of 5.60, when submitting a single-sided buy order at 5.50, your buy order may fail to execute because the 5.50 sell order is only part of a combination order;

4. Market lacks liquidity.