I gone through API documentation but i cannot found any of the API for creating new constant contact account.
I am trying to create new constant contact account from my C# code.
We do have an API that allows business partners to automate the process of creating and managing Constant Contact accounts. However, the SiteOwner API is a restricted access API provided to some Constant Contact Business Partners depending on the specific needs of the partner and the appropriateness of the API for those needs.
If you would like to apply as a business partner look further into getting set up for access to the SiteOwner API, you can begin here.
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Developer Homepage: http://developer.constantcontact.com/