public async Task <bool> IsPhoneNumberRegisteredAsync(string phoneNumber)
{
if (string.IsNullOrWhiteSpace(phoneNumber))
{
throw new ArgumentNullException(nameof(phoneNumber));
}
await ConnectAsync();
string normalizedPhoneNumber = phoneNumber.TrimStart('+');
AuthCheckedPhoneConstructor checkPhoneResult = await _client.CheckPhone(normalizedPhoneNumber);
return(checkPhoneResult.phoneRegistered);
}