I have gone through the forum, and forum and error_code documentation, and from that I undertand that this is related with xml malformed. But I can't figure out what's wrong with my xml. Could antone please help me?
After reviewing this XML, I find that it is most likely that the problem here is specifically that you are attempting to add contacts to a list that no longer exists. In this XML the contact is specifically being added to a list with the ID of 28, which is failing. In order to view the list IDs for all of the lists currently in your account, you can make a GET API request to https://api.constantcontact.com/ws/customers/USERNAME/lists
If you have any questions or any issues with updating the list ID, please let us know!