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

{
  "firstName": "Bastien",
  "lastName": "Velitchkine",
  "companyName": "Bastien VELITCHKINE EI",
  "jobTitle": "Growth Engineer",
  "companyDomain": "bvelitchkine.com",
  "email": "support@lemlist.com",
  "preferredContactMethod": "email",
  "industry": "Technology",
  "Company name": "Bastien Velitchkine",
  "_id": "lea_mizMsAEkRrJuhouYe",
  "isPaused": false,
  "campaignId": "cam_9NsHPnykWESTncCW8",
  "contactId": "ctc_Rofmb6uNGyaPNZ2ni",
  "emailStatus": "deliverable"
}