I am trying to enable web API in orocommerce. The documentation states to enable navigating to System Configuration > Application Settings > Web API config section. but my installation doesn't show the menu. I can only see
Are there any options to configure to make the menu visible?
You are referring to the documentation for OroCommerce 4.1. In the 3.1 version, that you are using, there is no setting, and web API is enabled by default.
For more details on using an API in 3.1, see Using Web Services API in OroCommerce 3.1 documentation article.