Add Field To Set Custom Page As Donation Page

/**

 * Create a new campaign field allowing to select the page where donations are made.

 */

add_action( 'init', function() {

	$campaign_field = new Charitable_Campaign_Field( 'donation_page', array(

		'label'      => 'Donation Page',

		'data_type'  => 'meta',

		'admin_form' => array(

			'type'     => 'select',

			'required' => false,

			'options'  => array(

				'default' => 'Use the default donation page',

				'pages'   => array(

					'options' => charitable_get_pages_options(),

					'label'   => 'Pages',

				),

			),

			'default'  => 'default',

			'section'  => 'campaign-donation-options',

		),

		'show_in_export' => true,

	) );

	/**

	 * Now, we register our new field.

	 */

	charitable()->campaign_fields()->register_field( $campaign_field );

} );

/**

 * Filter the page where users make donation to a campaign.

 *

 * @param  string $default The endpoint's URL.

 * @param  array  $args    Mixed set of arguments.

 * @return string

 */

add_filter( 'charitable_permalink_campaign_donation_page', function( $default, $args ) {

	/**

	 * Get the campaign object.

	 */

	$campaign_id = isset( $args['campaign_id'] ) ? $args['campaign_id'] : get_the_ID();

	$campaign    = charitable_get_campaign( $campaign_id );

	/**

	 * Get the campaign that received the campaign.

	 */

	if ( 'default' === $campaign->get( 'donation_page' ) ) {

		return $default;

	}

	return get_permalink( $campaign->get( 'donation_page' ) );

}, 10, 2 );