I need a URL for a paypal donation with the purpose field pre-populated

I assume you're POSTing data, correct? Below is a list of the fields that can be passed

https://www.paypal.com/cgi-bin/webscr?cmd=_pdn_xclick_prepopulate_outside

You can try adding the purpose field in that code as well, just add the html equivalent name to the list of hidden fields

Don't know about POSTing, I'm just creating a link that can be on a facebook post that someone can click on.

How EXACTLY is the field passed in?

I assumed you were creating a form and sending the data the way...

I was able to find the lit of variables (see link below) that can be used. Do a Ctrl-F on the page and search for "service" and that may give you direction.

https://developer.paypal.com/docs/classic/paypal-payments-standard/integration-guide/Appx_websitestandard_htmlvariables/

can you give an example of the link (take out the domain name) you have so far?

This is what I use now:
https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=WWJSGZXPU2DL4
(feel free to donate if you like hahahaha!)

It takes the user to the donation page, but I would like to somehow pass in some text that will populate the "Purpose" field.

Any ideas?

Hmmmm... that is good, but I think I need it to be editable, unless I can figure out how to put another field on that donation page where they can enter free form text.

I don't think you can make it editable, you're better off going into PayPal and adding an option free text field

OK,

I tired adding an option field by putting this in the advanced items box:
on1=Photonum

Then, I added this to the end of that URL:  &Photonum=1234

And while the word "Photonum:" showed up, the 1234 didn't show up anywhere.

If I put the following in the advanced items box:
on1=Photonum
os1=1234

Then the 1234 did show up after the word Photonum

I need a way to pass something in so I can see it when I look at the donation.  Any ideas?

I don't see any other field on the form, did you take it out?

this seems to be getting away from the original purpose of this question, which is to pre-populate the PURPOSE field, which we did. I'm not extremely familiar with building paypal forms, you may want to close this question down and ask a fresh one so that it gets some new eyes on it, or we can continue to try to piecemeal a solution for you, I'm fine either way.

Good point.  I'll do that.  You've been a big help.

You've been very helpful, thank you!

my pleasure! happy programming!