Why didn't the first SMS arrive? What are the reasons for not sending the first message?

The reasons why the first SMS might not have been received can vary:

1. Network issues — no signal, network overload, or temporary outages with the operator.
2. Incorrect recipient number — error in the number or formatting.
3. Blocking on the recipient's side — for example, blacklists or filtering settings.
4. Problems with the sender's SIM card or phone — malfunction, lack of balance, or restrictions.
5. Delays in message routing — technical failures at the operator's SMS center.
6. Lack of delivery confirmation — the message might have been sent but not delivered due to temporary issues.

For diagnostics, check the sending logs, delivery status, phone settings, and contact with the operator.