Hi @Rohansalwi ,

Try this

function onChange(control, oldValue, newValue, isLoading) {
    if (isLoading || newValue === '') {
        return;
    }
    alert(newValue);
    var firstChar = newValue[0].toUpperCase();

    if (firstChar == 'E') {
        g_form.setValue('billable_status', 'Billable');
    } else if (['P', 'I', 'O'].includes(firstChar)) {
        g_form.setValue('billable_status', 'Non-billable');
    } else {
        g_form.clearValue('billable_status');
    }
}

 I have added an alert statement just wanted to check if the client script is even triggering 

If it's coming please check if you have selected the correct variable name, catalog name,  type of client script in the client script. Please share the screenshot of the client script of it's not throwing the alert 

Regards 

Chaitanya