Just posting this so other users who are new to Snipcart do not have to waste their time like I had to.
In the docs it is not mentioned that you cannot use PayPal sandbox accounts for testing.
I got JS errors when I tried that and contacted the Snipcart team. Finally they confirmed that it is not possible to use sandbox accounts. They suggested to use live accounts for testing and then doing a refund for the test orders.
Testing of functionality is a vital part of developing any software. IMHO PayPal sandbox should be available for Snipcart testing.
At least it should be made clear in the docs that we cannot use sandbox accounts.
What do you think?