Why does sending text messages fail?

Regarding your first question, there are several possibilities:

1. The other party has set up a firewall. Your message was successfully sent, but others refused to receive it. Charge as usual, indicating that the delivery was successful, but the receipt received failed.

2. The other party's mobile phone is turned off, or there is no signal. The short message you sent was not received by the other party, but if the time exceeds the validity period of the short message set by the other party, you will also be prompted to send it successfully, but the receipt you received is a failure.

3. Communication problem, that is to say, it has nothing to do with the mobile phones of both parties. This may be caused by signal difference or communication error.

Secondly, as long as your mobile phone shows successful transmission, it will be charged. Whether the other party receives it or not. In other words, suppose you send a short message to a stopped number, as long as it is sent successfully, you will be charged.

Third, SMS is not local, long-distance or roaming. The cost of sending and receiving is the same. Then, how to calculate the SMS fee locally and how to calculate it abroad?