Right, just spent several hours trying to get fundraiser working and register the app. Before doing so decided to create a fundraiser (crowsourced t-shirts) and completed the setup and fundraiser as per instructions. It can be seen here
http://www.since1664.com/fundraisers/crowd-source-tee-shirt-test/ in sandbox mode
When I make my pledge, and fill in name and address and hit complete pledge, it takes me to http://www.since1664.com/fundraisers/crowd-source-tee-shirt-test/pledge/ and not to paypal. No pledge is recorded in the pledges table - in effect nothing is happening. The end result is I can't complete the app registration as it is not working in test mode!