Might want to see if the tests aren't broken, as well. They seem to be having trouble resolving the Key namespace.
Here's what happened with the CLI.
$ bin/nostr-php --content "Test of CLI" --key /home/.../nostr-private.key --relay wss://theforest.nostr1.com
PHP Fatal error: Uncaught Error: Typed property swentel\nostr\Relay\Relay::$payload must not be accessed before initialization in /home/.../nostr-php/src/Relay/Relay.php:87
Stack trace:
#0 /home/.../nostr-php/src/Application/Client.php(85): swentel\nostr\Relay\Relay->send()
#1 /home/.../nostr-php/bin/nostr-php(47): swentel\nostr\Application\Client->run()
#2 {main}
thrown in /home/.../nostr-php/src/Relay/Relay.php on line 87