Marking a Contact Marketable when adding a new contact

We are using XMLPRC API and legacy schema to create a contact record from our .NET app.
The Legacy schema doesn’t have any field related to OptIn. So all the contact records we add are shown as Non-Marketable.
How can we make the contact marketable when adding for the first time from the code.

Is there any way of making the existing contacts marketable (Current status is Non-Marketable) from the code instead of using “Action” option after selecting the contacts?

Greetings:

I think what you are looking for is the opt-in an Email Address api call. Check out the docs at https://developer.infusionsoft.com/docs/xml-rpc/#email-opt-in-an-email-address