Android phones are great, but you may face some issues from time to time. That's just part of the experience. One of the problems that may pop up is a connection problem or an invalid MMI code. 

You usually see this error when you are about to check your account balance, top-up, recharge, or perform any function designed by your SIM service provider, like adding a voucher to run a USSD code. What causes Connection Problem or Invalid MMI Code?

While the country's cell phone providers vary, invalid MMI code errors are usually found on dual SIM smartphones. The error pops up when the provider has some problems with the network or when there are SIM authentication issues. 

See also - Why does my phone say no service?

Ways to Fix Connection Problem or Invalid MMI Code

Method 1: Third-Party App

The best option, to begin with, is disabling some third-party apps. There are a lot of users who have found a solution by deleting an app that may have been causing the MMI code error. 

How can I be sure whether a third-party app is responsible for the connection problem or invalid MMI code? It's pretty simple. All you have to do is boot your Android device into Safe mode. 

What is Safe Mode?

Safemode on a device is very similar to a computer’s safe mode. In safe mode, the device does not load any third-party apps, only pre-installed ones. 

How to Enter Safe Mode

To enter safe mode and to find out if there’s a culprit app that may be interfering with the network operation of your phone, kindly follow the instruction below: 

• Press and hold the Power button on your device till you see the Power menu > Tap Power Off
• Press and hold the Power and Volume Down buttons at the same time to turn the device on. 
• Once the Samsung logo appears on the screen, you can let go of the power button. Ensure you keep holding the Volume Down Button
• Safe Mode will now appear at the bottom left of the screen.

How to Exit Safe Mode (3 Ways):

1. 1. Press and hold the Power button for at least 6 seconds, then tap Restart.
   2. Press and hold the Power + Volume Down buttons for at least 5 seconds
   3. Swipe down from the top of the screen to access the Notification Panel, then tap on "Safe mode is on" To disable and restart

Now it’s time to test.

• Enter the Prefix code within the dialer and see if it works eg “*135#
• If it works, then there is an app causing the Invalid MMI Code error on your Android phone.
• Reboot your phone and remove any recently installed apps. 

Method 2: Prefix code

Another simple and effective way to fix a connection problem or invalid MMI code on an Android phone is to add a comma at the end of the Prefix code.

For example:

If your Prefix code is *2904*7# then adding the comma at the end would do just the trick, which will look like *2904*7#,

OR

You can use the + symbol after * like *+2904*7#

The comma will force the operation to execute. This will overlook any error that's in the way.

Method 3: The Information mode

This method requires you to enter device information mode, activate Radio to Turn on IMS over SMS, and fix the connection problem or invalid MMI code error.

Enter information mode :

• Dial *#*#4636#*#* in the dialer
• Navigate to Device/Phone Information
• Click on "Run Ping Test "
• Then, tap on "Turn Off Radio."
• Next, click on "Turn on SMS over IMS."

 

Method 4: Reset Network Settings

Try resetting the network settings on your Android device. The process is simple. However, after performing this, you will have to adjust the options, add Wi-Fi passwords, pair the phone with Bluetooth devices, etc. To reset your network settings:

• Go to Settings
• Tap General Management. 
• Select Reset  
• Tap Reset network settings.

Method 5: Reset All Settings

Try resetting the network settings on your Android device. The process is simple. However, after performing this, you will have to adjust the options, add Wi-Fi passwords, pair the phone with Bluetooth devices, etc. To reset your network settings:

• Go to Settings
• Tap General Management. 
• Select Reset  
• Tap Reset settings.

Method 6: Network Operator

The next step to try would be to choose the network operator. Follow a few simple steps: 

• Navigate to Settings 
• Tap on Wireless & Networks Or Connections
• Select Mobile Networks 
• Select Network Mode 
• Tap on Search Now
• Then choose your network.

Method 7: Set Network Mode to Auto

Follow these steps:

• Go to Wireless & Networks Or Connections.
• Select Mobile Networks 
• Select Network Mode 
• You will get a pop-up menu with the different options you can choose from. Ensure that you select the first option that says 4G/3G/2G (auto connect).

Method 8: Update APN Settings

Consider updating your APN Settings. Under Wireless and Networks or Connection

• Navigate to Settings
• Tap Connections.
• Tap Mobile Networks
• Select Access Point Names
• Tap More (3 dots)
• Tap Reset to Default.
• Then enter the new APN Settings.

Read this guide:  Updated APN Settings For AT&T, Verizon, T-Mobile, Sprint ( +4 More)

 

Method 9: Activate SIM Card 

To enable your SIM card, Navigate to:

• Settings  
• Tap Connection. 
• SIM card manager > Tap one or both of the switches for the SIM or USIM cards to activate them.

 

Solution 10: Perform a Software Update

  Navigate to:

• Settings
• Scroll down to the extreme bottom
• Select Software Update
• Please wait for it to reboot and complete the update

Solution  11: Call your carrier

Consider calling your wireless carrier. Ask them if there is an issue with the carrier network. Otherwise, ask them for a SIM card replacement.

1. Ensure you have an active mobile data plan with your wireless carrier.

 

Read More on this 

1. What to do if your Android Phone is not downloading MMS
2. Why does my phone say no service
3. Android Not Receiving or Sending Texts
4. Is the Mobile Network available
5. Is your phone Registered on a Network
6. Android phones can't make or receive calls
7. APN settings for AT&T, Verizon, T-Mobile, Boost Mobile