I a using the exact code here https://developers.sendinblue.com/reference/addcontacttolist-1 to add a user to a list. It all works, user is created/updated (if exists) then the user is added to the list. However, when adding to the list it throws an error.
Error calling AddContactToList: {"code":"invalid_parameter","message":"Contact already in list and/or does not exist"}
Their code shows a display result in JSON which will never get hit because it throws at the Add method.
The error is straight-forward. The contact is already in the list and the API enforces uniqueness.
You can get the contacts that are already in the list via getContactsFromList
https://developers.sendinblue.com/reference/getcontactsfromlist
or contact details via getContactInfo:
https://developers.sendinblue.com/reference/getcontactinfo-1
So, you will need to check whether the contact is already in the list. If so, then don't add it. Otherwise, you can add it without problems.
