Проверьте, есть ли номер в WhatsApp

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://gate.whapi.cloud/contacts",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => "{\"contacts\":[\"447123456789\",\"447955033260\"]}",
  CURLOPT_HTTPHEADER => [
    "accept: application/json",
    "authorization: Bearer Your_Token",
    "content-type: application/json"
  ],
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

import requests

url = "https://gate.whapi.cloud/contacts"

payload = {
    "contacts": [
        "447123456789",
        "447955033260"
    ]
}
headers = {
    "accept": "application/json",
    "authorization": "Bearer Your_Token",
    "content-type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

const url = 'https://gate.whapi.cloud/contacts';

const response = await fetch(url, {
  method: 'POST',
  headers: {
    accept: 'application/json',
    authorization: 'Bearer Your_Token',
    'content-type': 'application/json',
  },
  body: JSON.stringify({
    contacts: ['447123456789', '447955033260'],
  }),
});

console.log(await response.text());

OkHttpClient client = new OkHttpClient();

MediaType mediaType = MediaType.parse("application/json");
RequestBody body = RequestBody.create(mediaType, "{\"contacts\":[\"447123456789\",\"447955033260\"]}");
Request request = new Request.Builder()
  .url("https://gate.whapi.cloud/contacts")
  .post(body)
  .addHeader("accept", "application/json")
  .addHeader("authorization", "Bearer Your_Token")
  .addHeader("content-type", "application/json")
  .build();

Response response = client.newCall(request).execute();

using RestSharp;

var options = new RestClientOptions("https://gate.whapi.cloud/contacts");
var client = new RestClient(options);
var request = new RestRequest("");
request.AddHeader("accept", "application/json");
request.AddHeader("Authorization", "Bearer Your_Token");
request.AddHeader("content-type", "application/json");
request.AddJsonBody(new { contacts = new[] { "447123456789", "447955033260" } });
var response = await client.PostAsync(request);

Console.WriteLine("{0}", response.Content);