Yes, there's an API, and many people know about it. What exactly is your question?

Hi Jay, thanks for reply.
I'm wondering how can we use APIs on Sage 300.
Is there any tool?

VB6, C# DotNet, and VB DotNet are the preferred languages.

I have visual studio 2015 on Sage 300 Server. is not not working with Sage 300 APIs?
or can I ask how can I open Sage 300 APIs with this tools?
if there are any manual, that will be great help.
Thanks for your help Jay.

Visual Studio is fine. You need to add a reference to the AccpacCOMAPI, then add a "using AccpacCOMAPI;" line to the top of your project. There is no manual for any of this. To get your code, record a VBA macro.

There are no manuals, unfortunately. www.tek-tips.com has a forum where some people have posted .Net code (www.tek-tips.com/links.cfm. Record a macro and convert to the code to your .Net language. Stephen Smith, Sage 300's prior Chief Software Architect has a blog with useful bits of code (smist08.wordpress.com/.../). Check over in the VBA forum (sagecity.na.sage.com/.../56).

Thanks all. Really appreciate help.
I'm totally new of Sage 300 and i will try some with these and ask again if i stuck somewhere.
Thanks again all!