How do I pass the amount and description to a PayPal Buy Now button?

I have generated a PayPal Buy Now button which leads to a payment page in which the user needs to enter the description and amount. However I would like to pass the amount and description directly to the button so the user does not have to add anything.

Below is the button code which I generated from PayPal. I added the currency_code and amount hidden fields but this is not passed through. I also need to pass the description.

Do I need to generate the button again? If so please advise on the selections.

		<form action="https://www.paypal.com/cgi-bin/webscr" method="post" target="_top"[embed=file 1448622]>
			<input type="hidden" name="cmd" value="_s-xclick">
			<input type="hidden" name="hosted_button_id" value="XXXNRYWVPXXX">
			<input type="hidden" name="currency_code" value="GBP">
			<input type="hidden" name="amount" value="22.99">
			<input type="image" src="https://www.paypalobjects.com/en_GB/i/btn/btn_paynowCC_LG.gif" border="0" name="submit" alt="PayPal – The safer, easier way to pay online!">
			<img alt="" border="0" src="https://www.paypalobjects.com/en_GB/i/scr/pixel.gif" width="1" height="1">
		</form>

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