<!DOCTYPE html>
<html>
<head>
<title>支付系统</title>
</head>
<body>
<h1>欢迎使用支付系统</h1>
<form action="/submit_payment" method="post">
<label for="username">用户名:</label>
<input type="text" id="username" name="username">
<label for="amount">支付金额:</label>
<input type="text" id="amount" name="amount">
<label for="payment_type">支付方式:</label>
<select id="payment_type" name="payment_type">
<option value="paypal">PayPal</option>
<option value=&#
