Crowdfunder don't charge non-profit organisations for platform fees. Instead, they ask each supporter for a tip.
When someone donates to your campaign, they can choose if they want to give a tip to Crowdfunder.
These tips are optional.
The website sets a tip of 10% or 20%, depending on the size of the donation. The person donating can set it to 0% if they want.
You may want to tell your supporters they can change the tip when they make their donation.