What is checksum?
1. Payment gateway have a mechanism to detect Fraudulent activities.
2. If any entity tries to hack during Payment process to change the price, Payment gateway will show a checksum error.
Below are the reasons for this error?
1. There could be virus in your customer's system.
2. Some entity actually hacking tries to hack.
3. Your Merchant Key/Salt key is incorrect. In this case, Please contact your Payment Gateway.