WPdonations: Add a New Custom field

gistfile1.php

// Add your own function to filter the fields
add_filter( 'submit_donation_form_fields', 'add_submit_donation_form_fields' );
 
// This is your function which takes the fields, modifies them, and returns them
// You can see the fields which can be changed in: includes/forms/class-wpdonations-form-submit-donation.php
function add_submit_donation_form_fields( $fields ) {
 
    // Here we register the new field
    $fields['donor']['donor_phone'] = array(
        'label'     	=> __('Phone', 'wpdonations'),
        'placeholder'   => _x('Phone', 'placeholder', 'wpdonations'),
        'type'  		=> 'text',
        'required' 		=> true,
        'priority' 		=> 6
        );
 
    // And return the modified fields
    return $fields;
}

// Hook function that save field(s) data
add_action( 'wpdonations_update_donation_data', 'frontend_add_fields_save', 10, 2 );

// Save field(s) data
function frontend_add_fields_save( $donation_id, $values ) {
    // Duplicate the following line for each new field added
	update_post_meta( $donation_id, '_donor_phone', $values['donor']['donor_phone'] );
}