curl --request POST \
  --url https://api.selfmailkit.com/v1/audiences/{audienceId}/contacts \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "email": "suppressionlist+9@simulator.amazonses.com",
  "is_subscribed": true,
  "first_name": "John",
  "last_name": "Doe"
}'

{
  "id": "01959faf-16e2-77dd-9585-cd25da58855e"
}