diff --git a/extension/background.js b/extension/background.js
index 745d6ef..43a6cd6 100644
--- a/extension/background.js
+++ b/extension/background.js
@@ -84,44 +84,50 @@ async function getCookieState() {
   return response;
 }
 
-// send ping to server, return response
+// send ping to server
 async function verifyConnection() {
   const path = 'api/ping/';
-  let response = await sendGet(path);
-  console.log('verify connection: ' + JSON.stringify(response));
+  let message = await sendGet(path);
+  console.log('verify connection: ' + JSON.stringify(message));
 
-  return response;
+  if (message?.response === 'pong') {
+    return true;
+  } else if (message?.detail) {
+    throw new Error(message.detail);
+  } else {
+    throw new Error(`got unknown message ${JSON.stringify(message)}`);
+  }
 }
 
 // send youtube link from injected buttons
-async function youtubeLink(youtubeMessage) {
-  let path;
-  let payload;
-
-  if (youtubeMessage.action === 'download') {
-    path = 'api/download/';
-    payload = {
+async function download(url) {
+  return await sendData(
+    'api/download/',
+    {
       data: [
         {
-          youtube_id: youtubeMessage.url,
+          youtube_id: url,
           status: 'pending',
         },
       ],
-    };
-  } else if (youtubeMessage.action === 'subscribe') {
-    path = 'api/channel/';
-    payload = {
+    },
+    'POST'
+  );
+}
+
+async function subscribe(url) {
+  return await sendData(
+    'api/channel/',
+    {
       data: [
         {
-          channel_id: youtubeMessage.url,
+          channel_id: url,
           channel_subscribed: true,
         },
       ],
-    };
-  }
-
-  let response = await sendData(path, payload, 'POST');
-  return response;
+    },
+    'POST'
+  );
 }
 
 async function cookieStr(cookieLines) {
@@ -172,33 +178,56 @@ async function sendCookies() {
   return response;
 }
 
-// process and return message if needed
+/*
+process and return message if needed
+the following messages are supported:
+type Message =
+  | { type: 'verify' }
+  | { type: 'cookieState' }
+  | { type: 'sendCookie' }
+  | { type: 'download', url: string }
+  | { type: 'subscribe', url: string }
+*/
 function handleMessage(request, sender, sendResponse) {
-  console.log('message background.js listener: ' + JSON.stringify(request));
+  console.log('message background.js listener got message', request);
 
-  if (request.verify === true) {
-    let response = verifyConnection();
-    response.then(message => {
-      sendResponse(message);
+  // this function must return the value `true` in chrome to signal the response will be async;
+  // it cannot return a promise
+  // so in order to use async/await, we need a wrapper
+  (async () => {
+    switch (request.type) {
+      case 'verify': {
+        return await verifyConnection();
+      }
+      case 'cookieState': {
+        return await getCookieState();
+      }
+      case 'sendCookie': {
+        return await sendCookies();
+      }
+      case 'download': {
+        return await download(request.url);
+      }
+      case 'subscribe': {
+        return await subscribe(request.url);
+      }
+      default: {
+        let err = new Error(`unknown message type ${JSON.stringify(request.type)}`);
+        console.log(err);
+        throw err;
+      }
+    }
+  })()
+    .then(value => sendResponse({ success: true, value }))
+    .catch(e => {
+      console.error(e);
+      let message = e?.message ?? e;
+      if (message === 'Failed to fetch') {
+        // chrome's error message for failed `fetch` is not very user-friendly
+        message = 'Could not connect to server';
+      }
+      sendResponse({ success: false, value: message });
     });
-  } else if (request.youtube) {
-    let response = youtubeLink(request.youtube);
-    response.then(message => {
-      sendResponse(message);
-    });
-  } else if (request.cookieState) {
-    let response = getCookieState();
-    response.then(message => {
-      sendResponse(message);
-    });
-  } else if (request.sendCookie) {
-    console.log('backgound: ' + JSON.stringify(request));
-    let response = sendCookies();
-    response.then(message => {
-      sendResponse(message);
-    });
-  }
-
   return true;
 }
 
diff --git a/extension/index.html b/extension/index.html
index f3f52dd..5dea72a 100644
--- a/extension/index.html
+++ b/extension/index.html
@@ -26,6 +26,7 @@
         <div class="submit">
             <button id="save-login">Save</button><span id="status-icon">&#9744;</span>
         </div>
+        <div id="error-out"></div>
         <hr>
         <p>Options:</p>
         <div class="options">
diff --git a/extension/popup.js b/extension/popup.js
index 9e591d5..a3c60ec 100644
--- a/extension/popup.js
+++ b/extension/popup.js
@@ -15,29 +15,52 @@ function getBrowser() {
       return chrome;
     }
   } else {
-    console.log('failed to dedect browser');
+    console.log('failed to detect browser');
     throw 'browser detection error';
   }
 }
 
+async function sendMessage(message) {
+  let { success, value } = await browserType.runtime.sendMessage(message);
+  if (!success) {
+    throw value;
+  }
+  return value;
+}
+
+let errorOut = document.getElementById('error-out');
+function setError(message) {
+  errorOut.style.display = 'initial';
+  errorOut.innerText = message;
+}
+
+function clearError() {
+  errorOut.style.display = 'none';
+}
+
 // store access details
 document.getElementById('save-login').addEventListener('click', function () {
   let url = document.getElementById('full-url').value;
   if (!url.includes('://')) {
     url = 'http://' + url;
   }
-  let parsed = new URL(url);
-  let toStore = {
-    access: {
-      url: `${parsed.protocol}//${parsed.hostname}`,
-      port: parsed.port || (parsed.protocol === 'https:' ? '443' : '80'),
-      apiKey: document.getElementById('api-key').value,
-    },
-  };
-  browserType.storage.local.set(toStore, function () {
-    console.log('Stored connection details: ' + JSON.stringify(toStore));
-    pingBackend();
-  });
+  try {
+    clearError();
+    let parsed = new URL(url);
+    let toStore = {
+      access: {
+        url: `${parsed.protocol}//${parsed.hostname}`,
+        port: parsed.port || (parsed.protocol === 'https:' ? '443' : '80'),
+        apiKey: document.getElementById('api-key').value,
+      },
+    };
+    browserType.storage.local.set(toStore, function () {
+      console.log('Stored connection details: ' + JSON.stringify(toStore));
+      pingBackend();
+    });
+  } catch (e) {
+    setError(e.message);
+  }
 });
 
 // verify connection status
@@ -52,6 +75,7 @@ document.getElementById('sendCookies').addEventListener('click', function () {
 
 function sendCookie() {
   console.log('popup send cookie');
+  clearError();
 
   function handleResponse(message) {
     console.log('handle cookie response: ' + JSON.stringify(message));
@@ -61,6 +85,7 @@ function sendCookie() {
 
   function handleError(error) {
     console.log(`Error: ${error}`);
+    setError(error);
   }
 
   let checked = document.getElementById('sendCookies').checked;
@@ -75,26 +100,26 @@ function sendCookie() {
   if (checked === false) {
     return;
   }
-  let sending = browserType.runtime.sendMessage({ sendCookie: true });
+  let sending = sendMessage({ type: 'sendCookie' });
   sending.then(handleResponse, handleError);
 }
 
 // send ping message to TA backend
 function pingBackend() {
-  function handleResponse(message) {
-    if (message.response === 'pong') {
-      setStatusIcon(true);
-      console.log('connection validated');
-    }
+  clearError();
+  function handleResponse() {
+    console.log('connection validated');
+    setStatusIcon(true);
   }
 
   function handleError(error) {
-    console.log(`Error: ${error}`);
+    console.log(`Verify got error: ${error}`);
     setStatusIcon(false);
+    setError(error);
   }
 
   console.log('ping TA server');
-  let sending = browserType.runtime.sendMessage({ verify: true });
+  let sending = sendMessage({ type: 'verify' });
   sending.then(handleResponse, handleError);
 }
 
@@ -105,6 +130,7 @@ function addUrl(access) {
 }
 
 function setCookieState() {
+  clearError();
   function handleResponse(message) {
     console.log(message);
     document.getElementById('sendCookies').checked = message.cookie_enabled;
@@ -115,10 +141,11 @@ function setCookieState() {
 
   function handleError(error) {
     console.log(`Error: ${error}`);
+    setError(error);
   }
 
   console.log('set cookie state');
-  let sending = browserType.runtime.sendMessage({ cookieState: true });
+  let sending = sendMessage({ type: 'cookieState' });
   sending.then(handleResponse, handleError);
   document.getElementById('sendCookies').checked = true;
 }
diff --git a/extension/script.js b/extension/script.js
index 7cbaf55..c9a511b 100644
--- a/extension/script.js
+++ b/extension/script.js
@@ -22,6 +22,14 @@ function getBrowser() {
   }
 }
 
+async function sendMessage(message) {
+  let { success, value } = await browserType.runtime.sendMessage(message);
+  if (!success) {
+    throw value;
+  }
+  return value;
+}
+
 const downloadIcon = `<svg version="1.1" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
 viewBox="0 0 500 500" style="enable-background:new 0 0 500 500;" xml:space="preserve">
 <style type="text/css">
@@ -362,18 +370,14 @@ function sendUrl(url, action, button) {
   function handleError(error) {
     console.log('error');
     console.log(JSON.stringify(error));
+    buttonError(button);
   }
 
-  let payload = {
-    youtube: {
-      url: url,
-      action: action,
-    },
-  };
+  let message = { type: action, url };
 
-  console.log('youtube link: ' + JSON.stringify(payload));
+  console.log('youtube link: ' + JSON.stringify(message));
 
-  let sending = browserType.runtime.sendMessage(payload);
+  let sending = sendMessage(message);
   sending.then(handleResponse, handleError);
 }
 
diff --git a/extension/style.css b/extension/style.css
index 5616465..72dcdac 100644
--- a/extension/style.css
+++ b/extension/style.css
@@ -76,4 +76,8 @@ hr {
 }
 .icons img {
     width: 25px;
-}
\ No newline at end of file
+}
+#error-out {
+    color: red;
+    display: none; /* will be made visible when an error occurs */
+}