Jmeter use random string inside CSV file and resolve at runtime

I have CSV File where I have stored full JSON Request and using this variable in API RQ - ${Request}

inside each row of the CSV File I have added ${randomVariable}

In my test plan I use randomVariable ${__RandomString(10,QWERTYUIOPASDFGHJKLZXCVBNM4563456345634_,)} this generates the random variable but in the JSON instead of actual random value its passed as ${randomVariable} I have tried using Beanshell PreProcessor with get and put but still doesn't work. Please help.