curl --request DELETE \
  --url https://api.lemlist.com/api/campaigns/{campaignId}/leads/{email} \
  --header 'Authorization: Basic <encoded-value>'

{
  "email": "john.doe@domain.com",
  "firstName": "John",
  "lastName": "Doe",
  "_id": "lea_7kMNQwplxvvD2hf5z",
  "isPaused": false,
  "campaignId": "cam_A1B2C3D4E5F6G7H8I9"
}