curl -L -X GET 'https://flux.postacksolutions.com/api/contacts/search?phoneNumber=%2B1234567890' \
  -H 'Authorization: Bearer YOUR_ACCESS_TOKEN'

{
  "users": [
    {
      "id": "6EAJHS27:user_123",
      "externalUserId": "user_123",
      "username": "john_doe",
      "email": "john@example.com",
      "phoneNumber": "+1234567890"
    }
  ]
}