Roger, I've done some more testing.  I noticed a couple of things.  In order to use the sandbox, you must be logged into developer.paypal.com first.  When I log into the developer.paypal.com first in another window, and then go through my DNN site with a purchase, it takes me to the sandbox site, but the url is not what you have above, its  "https://www.sandbox.paypal.com/us/cgi-bin/webscr?cmd=_flow&SESSION=wgydG5waSA5r6Cysr4ivHJQdI8tAGzFTaciB5lRoZGFhfWrnFs6xsyqz8rS&dispatch=5885d80a13c0db1f822cfe4b06d0ea2bc3deaf2f87c377c27f201b3d9033ed5c"

Now if I stay logged out of developer.paypal.com and go through my DNN site with a purchase, it takes me to a paypal sandbox site, but says "To access the Paypal sandbox, please login to Paypal Developer Central"  and the url at the top of my browser shows what you said should be up there.  Of course, at this point if I log in, I lose all that information in the url.

kind of a catch-22, it works if I stay logged out of developer.paypal.com, but i can't get into the sandbox to test.  If I sign in to developer.paypal.com, I can test my sandbox, but the url from dnn gets screwed up.   I suppose  this will work fine when I'm using the real paypal, and not the testing evironment, but by not being able to test it, my confidence isn't at 100%

still, its weird that this would work on my local test and not my live test

Mike,

I guessing at what is happening. When not logged into the sandbox, the URL isn't processed at all by PayPal. When you are logged in, it will be processed as if it was on live. PayPal is altering the URL and storing the information from it (presumably on a database, since they undoubtedly have a farm of servers), using the session/dispatch keys in the new url as a key to the data.

My point of checking the URL prior to logging into the sandbox, is to make sure all three URL's passed are correct (Return/Cancel/Notify). If they are, then the problem would appear to be at the PayPal end. If they aren't, then the problem is at your website end (Event module or Core). You can of course set this up on a production paypal site, as long at you can afford the cost of PayPal payments at about £0.21 to do the test. Just keep it secured from your end users.

If you want I can have a look at your live test site. Mail me on dnn at my lastname dot org dot uk

Roger

Are you having the same problem detailed here, where the return/cancel URLs are wrong? I tried to replicate this on a test site with Mike's help, so I could fix it, but couldn't replicate. If you can detail exactly how your site is set up, I can try to replicate again.

In any case you can test by changing the processor url in the Event Module settings under Enrollment Settings to www.sandbox.paypal.com. You will need to sign up for a developer account on the sandbox, but it's fairly easy to use.

Cheers
Roger