Problem
On your Soapbox Engage Donations app pages, you can choose to enable donors to cover the transaction fee. Sometimes, when a donor selects to cover the transaction fee, the total amount of their donation changes to $0.
Solution
Typically, this happens because the Transaction Fee Amount field hasn't been set for the Donations app page. When editing your page, to go Payment tab > Transaction Fee Coverage section, and set a value for the Transaction Fee Amount.