How to Fix 'Connection problem or invalid MMI code' when Running USSD code in any mobile phone

How to Fix 'Connection problem or invalid MMI code' error occurs in any mobile phone having any Network Providers (SIM). Are you getting the message 'Connection problem or invalid MMI code' whenever you are running the USSD code for checking balance, offers, recharge etc. Then this video will help you to fix the problem.
SOLUTION: You are running the USSD code in the area where there is no service or your Network operator is unavailable (No signal or out of coverage). Because, your phone is not registered on network. So, check whether your Network Operator is available in your area, that is scan for available Network operators.
This video can be the solution for 'Connection problem or invalid MMI code' occurs in any mobile phone including Samsung galaxy, micromax, sony xperia, moto g, asus, NEXUS etc & Network Operators including Airtel, Tata Docomo, Reliance, Idea, Aircel etc
Conclusion: To fix 'Connection problem or invalid MMI code', you need to fix 'No service - Selected Network (any Network Provider) Unavailable' or 'Mobile Network not available' and 'Not registered on Network'.