Donation Fee Calculation

/**

 * 2. Calculate the exact Stripe Fee (2.9% + .30) if "Yes" is selected

 */

add_filter( 'charitable_get_donation_amount', function( $amount, $data ) {

    if ( isset( $data['cover_fee_choice'] ) && 'yes' === $data['cover_fee_choice'] ) {

        // Reverse math formula: (Amount + Fixed Fee) / (1 - Percentage)

        $amount = ( $amount + 0.30 ) / ( 1 - 0.029 );

        $amount = round( $amount, 2 );

    }

    return $amount;

}, 10, 2 );