1. Run your phone in Safe mode Like Windows, Android phones also have a safe mode feature through which you can restart your phone in a type of diagnostic mode. In safe mode, only the built-in apps and system service run while all third-party apps that you download are disabled.
If an app is causing some issues (like crashing or freezing) in your phone, you can easily troubleshoot it by running safe mode. Apart from that, you can also fix connection problem or invalid MMI code error by using safe mode. 2. Downgrade network mode All 4G SIMs operate on LTE network mode. Connection problem and invalid MMI code error is mostly found in phones that have set LTE network mode as default. Luckily, Android phones have built-in settings in which you can change the network mode manually.
We would advise you to try this method also. So what you need to do is first go to the settings of your phone and click on the Connections there. Then go to Mobile networks and click the Network mode. Now you will see various network mode options. Select 3G/2G (auto connect). 3. Activate SMS over IMS In this method, we will turn on IMS over SMS feature from the Android testing menu. Just follow these simple steps – Dial *#*#4636#*#* in the dial-pad. It will open the Android testing menu. Go to Phone information and click Run Ping Test. Once the ping test is finished, click “Turn on Radio“. Next, click “Turn on SMS over IMS 4. Add Comma after USSD Another method by which you can fix the connection problem is very simple. All you need to do in this method is add the comma at the end of the USSD code you have dialed (for example: *121#,). Adding a comma at the end will force the operation to look for the error.
To add a comma, you have to tap and hold the star button. As an alternative, you can also use plus symbol for which you have to press the zero button. Both will do the same thing.
