I cannot get a range of selected text in a TextEdit application from my background application

My application is an agent type (running in the background), and I have a button in the window. when the user selects the text in TextEdit and triggers the action from my application, I need to get the range of the selection text. I am using below code, but I am getting below error

kAXErrorAttributeUnsupported

I am using the code below

AXUIElementRef systemWideElement = AXUIElementCreateSystemWide();
AXUIElementRef focussedElement = NULL;
AXError error = AXUIElementCopyAttributeValue(systemWideElement, kAXFocusedUIElementAttribute, (CFTypeRef *)&focussedElement);
if (error != kAXErrorSuccess) {
    NSLog(@"Could not get focussed element");
} else {
    AXValueRef selectedRangeValue = NULL;
    AXError getSelectedRangeError = AXUIElementCopyAttributeValue(focussedElement, kAXSelectedTextRangeAttribute, (CFTypeRef *)&selectedRangeValue);
    if (getSelectedRangeError == kAXErrorSuccess) {
        CFRange selectedRange;
        AXValueGetValue(selectedRangeValue, kAXValueCFRangeType, &selectedRange);
        AXValueRef selectionBoundsValue = NULL;
        AXError getSelectionBoundsError = AXUIElementCopyParameterizedAttributeValue(focussedElement, kAXBoundsForRangeParameterizedAttribute, selectedRangeValue, (CFTypeRef *)&selectionBoundsValue);
        CFRelease(selectedRangeValue);
        if (getSelectionBoundsError == kAXErrorSuccess) {
            CGRect selectionBounds;
            AXValueGetValue(selectionBoundsValue, kAXValueCGRectType, &selectionBounds);
            NSLog(@"Selection bounds: %@", NSStringFromRect(NSRectFromCGRect(selectionBounds)));
        } else {
            NSLog(@"Could not get bounds for selected range");
        }
        if (selectionBoundsValue != NULL) CFRelease(selectionBoundsValue);
    } else {
        NSLog(@"Could not get selected range");
    }
}
if (focussedElement != NULL) CFRelease(focussedElement);
CFRelease(systemWideElement);

In the code above getSelectedRangeError == kAXErrorAttributeUnsupported

Update: I work in a Sandboxed environment, the reason is that it does not work.