diff --git a/sdks/js/package.json b/sdks/js/package.json
index 3831b79..fd4f560 100644
--- a/sdks/js/package.json
+++ b/sdks/js/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@upnd/upend",
-  "version": "0.5.0",
+  "version": "0.5.1",
   "description": "Client library to interact with the UpEnd system.",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",
diff --git a/sdks/js/src/api.ts b/sdks/js/src/api.ts
index 2258dc3..83ea2c0 100644
--- a/sdks/js/src/api.ts
+++ b/sdks/js/src/api.ts
@@ -24,6 +24,7 @@ export type { AddressComponents };
 
 export type UpendApiError = {
   kind: "Unauthorized" | "HttpError" | "FetchError" | "Unknown";
+  message?: string;
   error?: Error;
 };
 
@@ -37,18 +38,18 @@ export class UpEndApi {
   private key: string | undefined;
   private readonly onError: ((error: UpendApiError) => void) | undefined;
 
-  constructor(config: {
+  constructor(config?: {
     instanceUrl?: string;
     wasmExtensions?: UpEndWasmExtensions;
     timeout?: number;
     authKey?: string;
     onError?: (error: UpendApiError) => void;
   }) {
-    this.setInstanceUrl(config.instanceUrl || "http://localhost:8093");
-    this.wasmExtensions = config.wasmExtensions;
-    this.timeout = config.timeout || 30_000;
-    this.key = config.authKey;
-    this.onError = config.onError;
+    this.setInstanceUrl(config?.instanceUrl || "http://localhost:8093");
+    this.wasmExtensions = config?.wasmExtensions;
+    this.timeout = config?.timeout || 30_000;
+    this.key = config?.authKey;
+    this.onError = config?.onError;
   }
 
   public setInstanceUrl(apiUrl: string) {
@@ -488,13 +489,11 @@ export class UpEndApi {
       });
       if (!result.ok) {
         if (result.status === 401) {
-          error = { kind: "Unauthorized" };
+          error = { kind: "Unauthorized", message: await result.text() };
         } else {
           error = {
             kind: "HttpError",
-            error: new Error(
-              `HTTP Error ${result.status}: ${result.statusText}`,
-            ),
+            message: `HTTP Error ${result.status}: ${result.statusText}`,
           };
         }
       }