curl --request POST \
  --url https://www.dench.com/api/v1/email/campaigns/{campaignId}/preview \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "sample": 5
}'

{
  "campaignId": "ecmp_abc123",
  "previews": [
    {
      "recipientId": "ecr_abc123",
      "to": "ada@lovelace.dev",
      "subject": "Hi Ada",
      "htmlBody": "<p>Hi Ada, saw your work at Lovelace Labs.</p>"
    }
  ]
}