JSFiddle - React, Tailwind, and code Playground

HTML

<form action="index.php">
    <input type="radio" name="pagto" value="A>">
    <input type="radio" name="pagto" value="B">
    <input type="radio" name="pagto" value="C">
    <input type="radio" name="pagto" value="D">
</form>

JavaScript

var radios = document.querySelectorAll('input[type="radio"]');
[].forEach.call(radios, function (radio) {
    radio.addEventListener('change', function () {
        document.querySelector('form').submit();
    });
});