What is the reason why BBK S7 can't send short messages?

First, check the settings in your SMS menu to see if the service center number has been changed. It should be +86 13800XYZ500, and +86 cannot be omitted. The XYZ in the middle is the area code, such as Beijing 100, Nanjing 250, Shanghai 2 10, Suzhou 5 12 and so on. If you still can't send it, then see if all the users around you can't send it. If you can, you can change your SIM card and try it on their mobile phones. If you can, it is not a network problem. If it still doesn't work, the SIM card may be damaged. You can take your ID card to the business hall to replenish it, but you may have to pay. The cost varies from place to place.