diff --git a/build.gradle b/build.gradle
index 3d7d47f..f4b2198 100644
--- a/build.gradle
+++ b/build.gradle
@@ -4,7 +4,7 @@ plugins {
 }
 
 group = 'de.winniepat'
-version = '0.0.8'
+version = '0.0.9'
 
 
 java {
diff --git a/src/main/java/de/winniepat/licenselib/LicenseClient.java b/src/main/java/de/winniepat/licenselib/LicenseClient.java
index 964f63e..a351f3a 100644
--- a/src/main/java/de/winniepat/licenselib/LicenseClient.java
+++ b/src/main/java/de/winniepat/licenselib/LicenseClient.java
@@ -75,6 +75,8 @@ public class LicenseClient {
             String licenseKey,
             String serverId
     ) {
+        URI uri = validateUrl(apiUrl);
+
         JsonObject payload = new JsonObject();
         payload.addProperty("plugin", plugin);
         payload.addProperty("licenseKey", licenseKey);
@@ -84,7 +86,7 @@ public class LicenseClient {
         }
 
         return HttpRequest.newBuilder()
-                .uri(URI.create(apiUrl))
+                .uri(uri)
                 .timeout(Duration.ofSeconds(10))
                 .header("Content-Type", "application/json")
                 .POST(HttpRequest.BodyPublishers.ofString(GSON.toJson(payload)))
@@ -92,7 +94,13 @@ public class LicenseClient {
     }
 
     private static LicenseResult errorResult(Throwable throwable) {
-        return new LicenseError(throwable.getMessage());
+        String msg = throwable.getMessage();
+
+        if (msg == null || msg.isBlank()) {
+            msg = throwable.getClass().getSimpleName();
+        }
+
+        return new LicenseError(msg);
     }
 
     private static String getString(JsonObject json, String key, String def) {
@@ -121,4 +129,18 @@ public class LicenseClient {
                 getString(json, "checkedAt", null)
         );
     }
+
+    private static URI validateUrl(String apiUrl) {
+        URI uri = URI.create(apiUrl);
+
+        if (uri.getScheme() == null || (!uri.getScheme().equals("http") && !uri.getScheme().equals("https"))) {
+            throw new IllegalArgumentException("Invalid URL scheme: " + apiUrl);
+        }
+
+        if (uri.getHost() == null) {
+            throw new IllegalArgumentException("Invalid URL (missing host): " + apiUrl);
+        }
+
+        return uri;
+    }
 }