Hello, Sage Peachtree 2010 SDK is now retired and no longer available for download. You have to upgrade your Peachtree instance to the latest version 2020 and then you can use the SDK for 2020. Please send your contact details including business name and address to [email protected] and we will have a Sage representative contact you with the upgrade options. Thanks!

The problem is SoumenS we are an ISV who sell a hospital management system. It is our costumers who use Peachtree accounting software to manage their finance. We can not force all of them to upgrade to Peachtree 2020 version.

It would be more fitting if we can get the SDK for 2010 version in this case.

You're probably officially in a bit of a Catch 22 situation NetTm. As SoumenS mentions, you're not going to get any official support. There may be someone on the boards that has a copy of the SDK they could share with you (though I'm sure that may not be officially legitimate, license wise).
If you are doing a .NET based integration, you can grab the Sage.Peachtree.API.dll file off of one of the customers machines (it can be the server or a client, both should have that file) and just pull that file in to a Visual Studio project and start coding. You'd need to get an authorization code from Sage to connect to live production databases, but I would expect your authorization code to work in 2010 as well as 2020 (though I don't know that to be a fact).

Thank you fuerstma. Is there any documentation related to Sage.Peachtree.API.dll?

Hey NetTm What you could do for documentation is grab the 2020 SDK (or a later version) and check out the Help file there. There will be a few functions/features available in the 2020 SDK that won't be available in the 2010, but it will be obvious when the function/method flat out isn't available. Not the best way to work, but it will do in a pinch. Such is the life of developing/support using out-of-support/old software.

SDK 2020.1 can be downloaded from KB 101670 - https://support.na.sage.com/selfservice/viewContent.do?externalId=101670. 

SDK 2020.1 can be downloaded from KB 101670 - https://support.na.sage.com/selfservice/viewContent.do?externalId=101670.