How do I add "client" identification to a Donate button?

[Treasurer521]

I'm trying to add a button (or 3) to a page for payment of dues in a club.  I started out with a donate button to get my feet wet but what I really want probably is 3 buttons, One to sign up for individual membership, one for family membership and one "donate" button for people who want to make a non standard payment, to be used if someone is generous or signing up for a prorated year.

I've been looking at this page: https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=developer/e_howto_html_Appx_websit... but  I don't see anything that would help.  

This is my sandbox test form:

Test sandbox
<form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" name="cmd" value="_s-xclick">
<input type="hidden" name="hosted_button_id" value="Q5N5BAT3BSWMQa">
<input type="image" src="https://www.sandbox.paypal.com/en_US/i/btn/btn_donateCC_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>

 I assume I can add another hidden input form element from the list on that page I referenced.  What I need to get back is a membership ID.I have that information available in a session variable and can populate the value of the element with JS.  

Thanks, for any help.

Jim.

[Treasurer521]

By the way, I found this answer to a similar question. "For a question as technical as this you may want to check the forums at PayPal's x.com. The forums there: https://www.x.com/docs/DOC-1613 have  a lot of great information." However I'm unable to post on those forums.  I'm logged in but the post new topic button says "login to post".  Fails in both FF and Chrome.  I'm stuck with getting help here.

Jim.

[PayPal_RobG]

Hello,

'custom' is the parameter you're looking for.

<input type="hidden" name="custom" value="the membership ID">

This will subsequently be return in the IPN (Instant Payment Notification) data.

Note: It will not show up in any reports though. For that you'd have to use a different parameter, such as "item_name".