Subscription flow (SMS_PIN)

1. CreateSubscription — create a subscription for the number. The response contains SubscriptionID, SubscriberAcceptanceChannel=SMS_PIN and status Pending.
2. ApproveSubscription — confirm the subscription with PIN 1234. A wrong code returns WRONG_PARAMS / InvalidPinCode with the attempts left; after the third one the subscription moves to ApprovingFailed and the correct PIN no longer helps.
3. The subscription becomes Active, and 15 seconds later a SubscriptionStatusNotification callback with EventType=APPROVED is sent.
4. GetSubscriptionStatus — check the status (SubscriptionStatus=Active); CancelSubscription — cancel: the status becomes Cancelled and an EventType=CANCELLED callback arrives.

<Request>
  <SubscriptionProjectID>2001</SubscriptionProjectID>
  <SubscriptionID>10000001</SubscriptionID>
  <PinCode>1234</PinCode>
  <Now>20260625120000</Now>
  <Signature>d2f36558ca5455be...</Signature>
</Request>

<Response>
  <StatusName>WRONG_PARAMS</StatusName>
  <ErrorReasonName>InvalidPinCode</ErrorReasonName>
  <ErrorDescription>Invalid PIN code, 2 attempt(s) left</ErrorDescription>
</Response>