expectedSignature = split(to_string!(.headers."x-hub-signature-256"), "=")[1]
actualSignature = encode_base16(hmac(to_string!(.body), to_string!(.secrets.SANDBOX_CLIENT_SECRET)))
if actualSignature != expectedSignature {
  null
} else {
  body = parse_json!(.body)
  value = body.entry[0].changes[0].value
  if !is_nullish(value.statuses) && length!(value.statuses) > 0 {
    value.statuses[0].recipient_id
  } else {
    value.contacts[0].wa_id
  }
}