public function validate( $valid ) {
		if ( ! $this->is_enabled() ) {
			return $valid;
		}

		// If $valid is already a truthy, return early since something else already encountered a validation issue.
		if ( $valid ) {
			return $valid;
		}

		// If we don't have a response to test, return an error and stop registration.
		$captcha = llms_filter_input_sanitize_string( INPUT_POST, 'cf-turnstile-response' );
		if ( ! $captcha ) {
			if ( apply_filters( 'llms_enable_recaptcha_logs', false ) ) {
				error_log( 'LifterLMS form blocked due to missing captcha' );
			}
			// Customize the error message displayed when a registration is blocked.
			llms_add_notice( __( 'Blocked.', 'lifterlms' ), 'error' );
			return true;
		}

		// Ok, try to validate the captcha.
		if ( isset( $_SERVER['HTTP_CF_CONNECTING_IP'] ) && filter_var( $_SERVER['HTTP_CF_CONNECTING_IP'], FILTER_VALIDATE_IP ) ) {
			// Use the CloudFlare IP if it exists.
			$ip = $_SERVER['HTTP_CF_CONNECTING_IP'];
		} else {
			$ip = $_SERVER['REMOTE_ADDR'];
		}
		$url_path      = 'https://challenges.cloudflare.com/turnstile/v0/siteverify';
		$data          = array(
			'secret'   => $this->secret_key,
			'response' => $captcha,
			'remoteip' => $ip,
		);
		$options       = array(
			'http' => array(
				'header'  => "Content-Type: application/x-www-form-urlencoded\r\n" .
							"User-Agent: PHP Script\r\n",
				'method'  => 'POST',
				'content' => http_build_query( $data ),
			),
		);
		$stream        = stream_context_create( $options );
		$result        = file_get_contents( $url_path, false, $stream );
		$response      = $result;
		$response_keys = json_decode( $response, true );

		if ( intval( $response_keys['success'] ) !== 1 ) {
			if ( apply_filters( 'llms_enable_spam_logs', false ) ) {
				error_log( 'LLMS_Turnstile verification failed: ' . print_r( $response, true ) );
			}

			llms_add_notice( __( 'Verification failed. Please try again.', 'lifterlms' ), 'error' );
			return true;
		}

		// We're okay to proceed.
		return $valid;
	}