public function retrieve_secure_strings() {

		$gateway_strings = $this->secure_strings;
		foreach ( $this->get_admin_settings_fields() as $field ) {

			if ( empty( $field['id'] ) || empty( $field['secure_option'] ) ) {
				continue;
			}

			$string = llms_get_secure_option( $field['secure_option'], '', $field['id'] );
			if ( empty( $string ) ) {
				continue;
			}

			$gateway_strings[] = $string;

		}

		/**
		 * Filters the list of the gateway's secure strings.
		 *
		 * @since 6.4.0
		 *
		 * @param string[] $gateway_strings List of secure strings for the payment gateway.
		 * @param string   $id              The gateway ID.
		 */
		$gateway_strings = apply_filters( 'llms_get_gateway_secure_strings', $gateway_strings, $this->id );

		return array_values( array_unique( $gateway_strings ) );

	}