Styjun

I'm just trying to get started with the sample addon Google describes here for extending the compose UI:
https://developers.google.com/gsuite/add-ons/gmail/extending-compose-ui

However when I run it I'm getting this error:

Error with the add-on. Run time error. Cannot return a card markup
from the callback function of a universal action.

I have not setup any universal actions in my manifest file:

 "timeZone": "America/New_York",
 "oauthScopes":[
 "https://www.googleapis.com/auth/script.send_mail",
 "https://www.googleapis.com/auth/gmail.readonly",
 "https://www.googleapis.com/auth/spreadsheets",
 "https://www.googleapis.com/auth/gmail.addons.execute",
 "https://www.googleapis.com/auth/gmail.addons.current.message.metadata",
 "https://www.googleapis.com/auth/gmail.modify",
 "https://www.googleapis.com/auth/gmail.addons.current.action.compose"
 ],
 "gmail":
 "name": "My Mail Merge",
 "logoUrl": "https://www.gstatic.com/images/icons/material/system/1x/label_googblue_24dp.png",
 "composeTrigger": 
 "draftAccess": "METADATA",
 "selectActions": [
 
 "text": "show UI",
 "runFunction": "buildImageComposeCard"
 
 ]
 ,
 "openLinkUrlPrefixes": [
 "https://mail.google.com/"
 ],
 "primaryColor": "#42585F4",
 "secondaryColor": "#42585F4"
 ,
 "exceptionLogging": "STACKDRIVER"

Below is Code.gs:

function getInsertImageComposeUI(e) 
 return [buildImageComposeCard()];


function buildImageComposeCard() 
 // Get a list of image URLs to display in the UI.
 // This function is not shown in this example.
 var imageUrls = [
 "https://mail.google.com/1",
 "https://mail.google.com/2",
 "https://mail.google.com/3"
 ];

 var card = CardService.newCardBuilder();
 var cardSection = CardService.newCardSection().setHeader('My Images');
 for (var i = 0; i < imageUrls.length; i++) 
 var imageUrl = imageUrls[i];
 cardSection.addWidget(
 CardService.newImage()
 .setImageUrl(imageUrl)
 .setOnClickAction(CardService.newAction()
 .setFunctionName('applyInsertImageAction')
 .setParameters('url' : imageUrl)));
 
 return card.addSection(cardSection).build();


function applyInsertImageAction(e) 
 var imageUrl = e.parameters.url;
 var imageHtmlContent = '<img style="display: block" src="'
 + imageUrl + '"/>';
 var response = CardService.newUpdateDraftActionResponseBuilder()
 .setUpdateDraftBodyAction(CardService.newUpdateDraftBodyAction()
 .addUpdateContent(
 imageHtmlContent,
 CardService.ContentType.HTML)
 .setUpdateType(
 CardService.UpdateDraftBodyType.IN_PLACE_INSERT))
 .build();
 return response;

In the manifest file, runFunction has to be set to "getInsertImageComposeUI",

Also, in the code file, CardService.ContentType.HTML has to be one of

CardService.ContentType.MUTABLE_HTML

or

CardService.ContentType.IMMUTABLE_HTML