Error: Class "Websocket\Client" not found

I feel like this should not be so difficult, but I'm struggling with it for almost the entire day, so I'm asking for help!

I installed a websocket client with composer like this: 

Code:

composer require textalk/websocket

I use IntelliJ, and when I add

PHP Code:

use Websocket\Client; 


 and then initiate a connection with

PHP Code:

$wsClient = new Client($URL);  


there are no IDE errors indicated regarding any missing dependencies.  However, when I run the code, I get an error Class "Websocket\Client" not found.  

I have located all of the needed files in vendor/textalk folder, checked all autoload files exist, but I just don't know where to go from here. 
Thanks in advance!!!