Why did my limit order execute immediately?

A limit order allows traders to set a specific execution price. Compared to market orders, limit orders provide traders with better control over the buy or sell price of their positions, at the expense of guaranteeing order execution.

The main reason a limit order executes immediately is as follows:

When the user's limit price matches the best available price (a price favorable to the user), the limit order will execute immediately.
For example:
Buy order = Order price is higher than the best available sell price
Sell order = Order price is lower than the best available buy price