Get value of contact form 7 radio button [closed]

I have following radio buttons in contact form 7 and a few text fields and hidden fields.

[radio radio id:radio label_first "3" "6" "9" "12"]

Following are a few example lines of code in functions.php. I am able to get all the other values e.g text fields and hidden fields but not radio buttons.

function wpcf7_cstm_function($contact_form) {
    $title = $contact_form->title;
    $submission = WPCF7_Submission::get_instance();

    if ($submission) {
        $posted_data = $submission->get_posted_data();
    }
$txt = $posted_data['txt'];
        $text2 = $posted_data['txt2'];
$radio=$posted_data['radio']; 
}

Is there a way to get the value of selected radio button?

Depending when you’d like to take the action you should change the hook – I’ve chosen wpcf7_before_send_mail – your function

function wpcf7_cstm_function($contact_form) {
    $title = $contact_form->title;
    $submission = WPCF7_Submission::get_instance();

    if ($submission) {
        $posted_data = $submission->get_posted_data();

        $txt = isset($posted_data['txt'])?$posted_data['txt']:'';
        $text2 = isset($posted_data['txt2'])?$posted_data['txt2']:'';
        $radio = isset($posted_data['radio'][0])?$posted_data['radio'][0]:'';

        // do something with your data
    }
}
add_action("wpcf7_before_send_mail", "wpcf7_cstm_function");

Explanation: radio buttons (like checkboxes) are returned in a form on an array. Radio values are one-element arrays, so you retrieve them by accessing the first element of the array. For checkboxes you’d have to iterate over the whole returned array to get all the values.