<?php 
$balance = invoice_balance($invoice) ;
$invoicenum = invoice_id($invoice) ; 
$paypalemail = "[email protected]" ;
$link = ("https://www.paypal.com/cgi-bin/webscr?cmd=_xclick&currency_code=USD&business=$paypalemail&amount=$balance&tax=0&item_name=Invoice $invoicenum");
echo "<p>Pay securely with credit or debit card - <a href='$link' target=_blank >Click Here</p>";
echo '<img src="http://www.paypalobjects.com/WEBSCR-640-20110401-1/en_US/i/bnr/horizontal_solution_PP.gif"" border=0>';
?>

http://www.myclientbase.com/forums/viewtopic.php?f=3&t=755&p=3387&hilit=paypal#p3387

_PHP Snippet for Paying via Paypal_

This snippet is designed for most open source invoicing applications that you have control over the template setup. There multiple free or open source PHP applications that you can download server-side and implement this snippet at the bottom or very top of the template. Work great on *MyClientBase*.

PHP Pay via Paypal (for most Open Source Invoicing Apps)

php, api

PHP