Error upon using demo

[Trent Wiles]

Ran the last demo, ran into an interesting error:

PHP Fatal error:  Declaration of Smalot\\Cups\\Transport\\Client::sendRequest(Psr\\Http\\Message\\RequestInterface $request) must be compatible with Psr\\Http\\Client\\ClientInterface::sendRequest(Psr\\Http\\Message\\RequestInterface $request): Psr\\Http\\Message\\ResponseInterface in /var/www/html/vendor/smalot/cups-ipp/src/Transport/Client.php on line 22

[krutraf]

i have the same error:
Fatal error: Declaration of Smalot\Cups\Transport\Client::sendRequest(Psr\Http\Message\RequestInterface $request) must be compatible with Psr\Http\Client\ClientInterface::sendRequest(Psr\Http\Message\RequestInterface $request): Psr\Http\Message\ResponseInterface in /var/www/html/vendor/smalot/cups-ipp/src/Transport/Client.php on line 119

installed nginx+php7.4-fpm

[Pierre]

Same error