Don't rely on app()->joinPaths(), which is not available in Laravel 9.

src/Support/Domain.php

@@ -54,9 +54,7 @@ public function __construct(string $domain, string $subdomain = null)
 
         $this->namespace = DomainNamespaces::from($this->domain, $this->subdomain);
 
-        $this->path = str(app()->joinPaths(config('ddd.paths.domains'), $this->domainWithSubdomain))
-            ->replace(['\\', '/'], DIRECTORY_SEPARATOR)
-            ->toString();
+        $this->path = Path::join(config('ddd.paths.domains'), $this->domainWithSubdomain);
     }
 
     protected function getDomainBasePath()
@@ -76,7 +74,7 @@ public function path(string $path = null): string
             ->append('.php')
             ->toString();
 
-        return app()->joinPaths($this->path, $path);
+        return Path::join($this->path, $path);
     }
 
     public function relativePath(string $path = ''): string

src/Support/Path.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace Lunarstorm\LaravelDDD\Support;
+
+class Path
+{
+    public static function normalize($path)
+    {
+        return str_replace(['\\', '/'], DIRECTORY_SEPARATOR, $path);
+    }
+
+    public static function join(...$parts)
+    {
+        $parts = array_map(function ($part) {
+            return trim(static::normalize($part), DIRECTORY_SEPARATOR);
+        }, $parts);
+
+        return implode(DIRECTORY_SEPARATOR, $parts);
+    }
+}