Allow Zero Dollar Donations

/**

 * Allow people to "donate" $0.

 */

function ed_charitable_set_minimum_donation_amount() {

    return 0;

}

add_filter( 'charitable_minimum_donation_amount', 'ed_charitable_set_minimum_donation_amount' );

/**

 * You need to specifically enable $0 donations.

 */

add_filter( 'charitable_permit_0_donation', '__return_true' );