messages['error'], 'error' );
				$log->error( sprintf( 'Form %d > Mailchimp API error: %s %s', $form->ID, $error_code, $error_message ) );

				/**
				 * Fire action hook so API errors can be hooked into.
				 *
				 * @param MC4WP_Form $form
				 * @param string $error_message
				 */
				do_action( 'mc4wp_form_api_error', $form, $error_message );
			}

			// bail
			return;
		}

		// Success! Did we update or newly subscribe?
		if ( $result->status === 'subscribed' && $result->was_already_on_list ) {
			$form->last_event = 'updated_subscriber';
			$form->add_notice( $form->messages['updated'], 'success' );
			$log->info( sprintf( 'Form %d > Successfully updated %s', $form->ID, $data['EMAIL'] ) );

			/**
			 * Fires right after a form was used to update an existing subscriber.
			 *
			 * @since 3.0
			 *
			 * @param MC4WP_Form $form Instance of the submitted form
			 * @param string $email
			 * @param array $data
			 */
			do_action( 'mc4wp_form_updated_subscriber', $form, $subscriber->email_address, $data );
		} else {
			$form->last_event = 'subscribed';
			$form->add_notice( $form->messages['subscribed'], 'success' );
			$log->info( sprintf( 'Form %d > Successfully subscribed %s', $form->ID, $data['EMAIL'] ) );

			/**
			 * Fires right after a form was used to add a new subscriber.
			 *
			 * @since 4.8.13
			 *
			 * @param MC4WP_Form $form Instance of the submitted form
			 * @param string $email
			 * @param array $data
			 */
			do_action( 'mc4wp_form_added_subscriber', $form, $subscriber->email_address, $data );
		}

		/**
		 * Fires right after a form was used to add a new subscriber (or update an existing one).
		 *
		 * @since 3.0
		 *
		 * @param MC4WP_Form $form Instance of the submitted form
		 * @param string $email
		 * @param array $data
		 * @param MC4WP_MailChimp_Subscriber[] $subscriber
		 */
		do_action( 'mc4wp_form_subscribed', $form, $subscriber->email_address, $data, $map );
	}

	/**
	 * @param MC4WP_Form $form
	 */
	public function process_unsubscribe_form( MC4WP_Form $form ) {
		$mailchimp = new MC4WP_MailChimp();
		$log       = $this->get_log();
		$result    = null;
		$data      = $form->get_data();

		// unsubscribe from each list
		foreach ( $form->get_lists() as $list_id ) {
			$result = $mailchimp->list_unsubscribe( $list_id, $data['EMAIL'] );
		}

		if ( ! $result ) {
			$form->add_notice( $form->messages['error'], 'error' );
			$log->error( sprintf( 'Form %d > Mailchimp API error: %s', $form->ID, $mailchimp->get_error_message() ) );

			// bail
			return;
		}

		// Success! Unsubscribed.
		$form->last_event = 'unsubscribed';
		$form->add_notice( $form->messages['unsubscribed'], 'notice' );
		$log->info( sprintf( 'Form %d > Successfully unsubscribed %s', $form->ID, $data['EMAIL'] ) );

		/**
		 * Fires right after a form was used to unsubscribe.
		 *
		 * @since 3.0
		 *
		 * @param MC4WP_Form $form Instance of the submitted form.
		 * @param string $email
		 */
		do_action( 'mc4wp_form_unsubscribed', $form, $data['EMAIL'] );
	}

	/**
	 * @param MC4WP_Form $form
	 */
	public function respond( MC4WP_Form $form ) {
		$success = ! $form->has_errors();

		if ( $success ) {

			/**
			 * Fires right after a form is submitted without any errors (success).
			 *
			 * @since 3.0
			 *
			 * @param MC4WP_Form $form Instance of the submitted form
			 */
			do_action( 'mc4wp_form_success', $form );
		} else {

			/**
			 * Fires right after a form is submitted with errors.
			 *
			 * @since 3.0
			 *
			 * @param MC4WP_Form $form The submitted form instance.
			 */
			do_action( 'mc4wp_form_error', $form );

			// fire a dedicated event for each error
			foreach ( $form->errors as $error ) {

				/**
				 * Fires right after a form was submitted with errors.
				 *
				 * The dynamic portion of the hook, `$error`, refers to the error that occurred.
				 *
				 * Default errors give us the following possible hooks:
				 *
				 * - mc4wp_form_error_error                     General errors
				 * - mc4wp_form_error_spam
				 * - mc4wp_form_error_invalid_email             Invalid email address
				 * - mc4wp_form_error_already_subscribed        Email is already on selected list(s)
				 * - mc4wp_form_error_required_field_missing    One or more required fields are missing
				 * - mc4wp_form_error_no_lists_selected         No Mailchimp lists were selected
				 *
				 * @since 3.0
				 *
				 * @param   MC4WP_Form     $form        The form instance of the submitted form.
				 */
				do_action( 'mc4wp_form_error_' . $error, $form );
			}
		}

		/**
		 * Fires right before responding to the form request.
		 *
		 * @since 3.0
		 *
		 * @param MC4WP_Form $form Instance of the submitted form.
		 */
		do_action( 'mc4wp_form_respond', $form );

		// do stuff on success (if form was submitted over plain HTTP, not for AJAX or REST requests)
		if ( $success && ! $this->request_wants_json() ) {
			$redirect_url = $form->get_redirect_url();
			if ( ! empty( $redirect_url ) ) {
				wp_redirect( $redirect_url );
				exit;
			}
		}
	}

	private function request_wants_json() {
		if ( isset( $_SERVER['HTTP_ACCEPT'] ) && false !== strpos( $_SERVER['HTTP_ACCEPT'], 'application/json' ) ) {
			return true;
		}

		return false;
	}

	/**
	 * @return MC4WP_API_V3
	 */
	protected function get_api() {
		return mc4wp( 'api' );
	}

	/**
	 * @return MC4WP_Debug_Log
	 */
	protected function get_log() {
		return mc4wp( 'log' );
	}
}