The Sage 300 web API is for use with any language. It isn't specifically for the web UI. I use it all the time for various projects so that I can integrate 3rd party software with Sage 300. It's pretty straightforward to use. Which version of Sage are you using? The URL you posted suggests Sage 2017. I've used the web API from 2018 upwards.

Correct! The Sage 300 Web API is installed when the Sage 300 Web Screens are installed and that is the only reliance on the web screens. Since the Web API uses the Sage 300 .NET API under the covers it is just another API to bring data in and out of the application. 

I am using desktop version of sage and it don't works on chrome or any other web browser, it works as other windows application. Now if my sage doesn't work on web then will it be possible to use those API?

Installing the web screens for Sage 300 does not mean that you have to use them. Of course, it does mean that IIS, MSMQ, etc. are installed and configured correctly. But, because the Web API gets installed when the Sage 300 Web Screens are installed, there s=is that association. We will be looking to "un-couple" that in the future so that the Web API can be it's own selection in the installer. But, that is forward thinking at this point.

Once installed, even though the web screens are not being used, the Web API can be used. Note, that there are Security groups (Sage 300 Web API) that must be associated to the user accessing the Web API.

Hi John Thanks for the insight.
We are using Sage 300 2019 . I will install the Web Screen in order to access the Web API.
In the meantime however, can you point me to the most uptodate documentation for the Web API? 
Thanks in advance

The Web API uses Swagger (Open API). So, when you run localhost/Sage300WebApi, you will land on the landing page where you have a button to launch the web api. At that point, all of the endpoints are presented and you can interact with them. Note: Be sure to setup a user with the proper access and security groups first.

in the Web SDK, we have documentation in the docs/webapi folder and there are C# samples to integrate with the web api in the samples folder. The open source web SDK is located at https://github.com/SageNADev/sage300-sdk and for the 2019 release, you will want the "release-2019" branch.

thanks John. that is great to hear.  The web API is much easier and uncoupling giving us options...less is more.