贝宝支付按钮-你可以动态设置价格

我当然对使用PayPal的标准支付按钮感兴趣；然而，我希望能够在代码中自己设置金额，而不是被迫通过Paypal创建一个固定金额的按钮。例如，我认为以下代码可以工作：

<form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post" target="_top">
<input type="hidden" name="cmd" value="_s-xclick">
<input type="hidden" name="amount" value="5.00">
<input type="hidden" name="encrypted" value="-----BEGIN PKCS7-----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-----END PKCS7-----
">
<input type="image" src="https://www.sandbox.paypal.com/en_US/i/btn/btn_buynowCC_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
<img alt="" border="0" src="https://www.sandbox.paypal.com/en_US/i/scr/pixel.gif" width="1" height="1">
</form>

这也不起作用：

<form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post" target="_top">
<input type="hidden" name="cmd" value="_s-xclick">
<input type="hidden" name="hosted_button_id" value="U7K937HLYPW6L">
<input type="hidden" name="amount" value="5.00">
<input type="image" src="https://www.sandbox.paypal.com/en_US/i/btn/btn_buynowCC_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
<img alt="" border="0" src="https://www.sandbox.paypal.com/en_US/i/scr/pixel.gif" width="1" height="1">
</form>

该页面允许用户输入自己的金额，而不是将用户引导到可以支付5.00的页面。在我的实际应用程序中，我会使用PHP来计算总额（在cart样式的页面上），并将该值与"amount"键相关联，但即使使用静态值，我也无法使其工作。解决方案是什么？

非常感谢！