When creating a new subscriber, Buttondown will now reject the request if a subscriber with the same email address already exists, even if that subscriber has unsubscribed or is otherwise in a "valid" state. We do this to protect the data and history of existing subscribers.

However, if you're looking for behavior more akin to an upsert, you can provide a X-Buttondown-Collision-Behavior header of overwrite or add in the request header:

import requests

url = "https://api.buttondown.com/v1/subscribers"
headers = {
  "Authorization": "Token $BUTTONDOWN_API_KEY",
  "X-Buttondown-Collision-Behavior": "overwrite"
}
data = {
  "email_address": "john@example.com",
  "tags": [
    "newsletter-1",
    "newsletter-2"
  ]
}

response = requests.request("POST", url, headers=headers, json=data)
print(response.text)

This is a slightly nuanced decision for you to make as an API caller; we've explained more about our default behavior and reasoning in the API endpoint docs.