Hello, 
We just bought this Plugin and it seems it ist currently incompatible with PHP 7.3.1. I am getting the following error:
| Code: | 
| 
 strpos(): Non-string needles will be interpreted as strings in the future. Use an explicit chr() call to preserve the current behavior
 | 
| Code: | 
| 
 /wp-content/plugins/ari-stream-quiz/libraries/plugin-update-checker/plugin-update-checker.php
 
 /**
 * Check if the plugin file is inside the mu-plugins directory.
 *
 * @return bool
 */
 protected function isMuPlugin() {
 static $cachedResult = null;
 
 if ( $cachedResult === null ) {
 //Convert both paths to the canonical form before comparison.
 $muPluginDir = realpath(WPMU_PLUGIN_DIR);
 $pluginPath  = realpath($this->pluginAbsolutePath);
 
 $cachedResult = (strpos($pluginPath, $muPluginDir) === 0); /*<---- This Line throws the error */
 }
 
 return $cachedResult;
 }
 
 | 
I found a workaround for now, disabled error-reporting, but it would be nice if this could be fixed in a future Version. 
Regards,