Xiaomi mobile phone can receive short messages, but can't send them. It always shows why it was sent.

It is recommended that you check the following steps for troubleshooting.

1 Check whether SMS sending and receiving are normal or whether the number of SMS center is correct. (Telecom version does not need to set SMS center number)

2 Turn on the option of always receiving MMS. (System Settings >> "All Settings" > >; "mobile network" > >; "Always accept MMS")

Ask the operator whether to open the mobile Internet service. MMS can only be sent successfully if it has the function of "surfing the Internet by mobile phone", but it will not generate traffic charges, and operators will charge according to the number of messages.

4 Whether the selected attachment is too large, operators generally have strict size restrictions on the pictures sent by MMS. Please consult the operator for details.

I suggest you change the sim card of different operators and try to send it.

It is recommended that you back up your data, then clear all the data, upgrade to the latest version of miui development, and then try to send it.

If the problem is not solved, please go to the maintenance point near you for maintenance inspection/service/back station.