curl --request GET \
  --url https://api.embedreach.com/api/subscriptions/{externalId}

{
  "success": true,
  "message": "<string>",
  "data": {
    "externalId": "<string>",
    "emailOptOut": true,
    "phoneOptOut": true,
    "emailSubscriptionChangeSource": "<string>",
    "smsSubscriptionChangeSource": "<string>",
    "emailSubscriptionChangeAt": "<string>",
    "smsSubscriptionChangeAt": "<string>",
    "lastSubscriptionChangeAt": "<string>"
  }
}