echo '<form method="post" action="https://bank.com/payment">';
echo '<input type="hidden" name="order_id" value="1">';
echo '<input type="hidden" name="amount" value="1000">';
echo '<input type="submit" value="Отправить платеж">';
echo '</form>';
<?php
echo '<form style="display: none;" method="post" action="https://bank.com/payment">';
echo '<input type="hidden" name="order_id" value="1">';
echo '<input type="hidden" name="amount" value="1000">';
echo '<input type="submit" value="Отправить платеж">';
echo '</form>';
echo '<script> document.querySelector("form").submit(); </script>';