Payments is not working

Hi, im working with crowdfunding plugin with Fundity theme, also i have enabled the easy dowload plugin.
It all worsk until i try to “donate” for a campaigns. When i type a pledge amount (Example $20) it redirects me to paypal to follow the purchase, but there i can see the amount is 0. When i try to update the change (again $20) it gives me an error. ANyone can help me on this?

Here is the link of the website:

https://www.ads-software.com/plugins/appthemer-crowdfunding/