When developing an application that uses PayPal for payment processing, here are a few things that you might like to know about their test (or sandbox) environment that isn't necessarily the same in their live environment.
- Don't try and approve any amount over $1,000.00; you can, but it'll give you a bogus reply.
- Only use 123 for the credit card's CCV
- Only use 4 digit expiration dates (mmyy) - this is true for live as well
Hope it helps!
(Hat tip to Mike Dopp for pointing these out!)