I know Phortune is a prototype, but this is a pretty simple issue, and it has a pretty simple fix.
Basically all Paypal transactions are sent to the sandbox site regardless of the mode set on the provider.
Basically you can't make a payment to paypal, at all.
Create a new paypal merchant account,
Fill in all the required info, and set the mode to Live,
Make a new initiative in Fund, try and back it using paypal,
You will be sent to sandbox.paypal.com and get an error.
It should omit the sandbox part if the provider is in live mode.